Itp 120 Chapt 19 2009 Binary Input & Output

Chapter 19 Chapter 19 Binary Input & Output Binary Input & Output

Java I ITP 120 Java I ITP 120

ITP 120 Java Programming I2

Patrick Healy

Class #15 – Input and Output Chapter Objectives

To understand how I/O is handled in Java To distinguish between text I/O and binary I/O To read and write bytes using FileInputStream and FileOutputStream To read and write primitive values and strings using the DataInputStream and

DataOutputStream classes To store and restore objects using ObjectOutputStream and ObjectInputStream, and

to understand how objects are serialized and what kind of objects can be serialized To use the Serializable interface to enable objects to be serializable (optional) To know how to serialize arrays (optional) To use RandomAccessFile for both read and write (Optional).


Patrick Healy

Class #15 – Input and Output Overview

The java.io.* package provides a library of classes to read and write various types of data.

In Java, all data I/O is handled in the form of streams Data streams can be byte streams or character streams The java.io package has classes that process byte streams of all types NOTE: In Java, a character is 2 BYTES ! Also NOTE: a Unicode character is 2 bytes ! The Reader and Writer classes process character streams. Streams can be layered, so that one type of streams can be converted

to another type of streams by chaining. Chaining a character stream reader to a byte stream reader to read bytes on one end and produce characters at the other end .


Patrick Healy

Class #15 – Input and Output

Overview --- Streams

A stream is an abstraction of a continuous one-way flow of data.

Program

Output Stream

File

Input Stream


Patrick Healy


2 Types of Stream Classes: Bytes & Characters

The stream classes can be categorized into two types: byte streams and character streams.

The InputStream/OutputStream class is theroot of all BYTE stream classes

The Reader/Writer class is the root of all CHARACTER streamclasses.

The subclasses of InputStream/OutputStream are analogous to the subclasses of Reader/Writer.


Patrick Healy


Byte Stream Classes (note: the word “stream” )

InputStream

OutputStream

RandomAccessFile

Object

PipeOutputStream

SequenceInputStream

StringBufferInputStream

ByteArrayOutputStream

ObjectOutputStream

FilterOutputStream

FileOutputStream

PipedInputStream

PushBackInputStream

BufferedInputStream

LineNumberInputStream

DataInputStream

BufferedOutputStream

DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

ByteArrayInputStream InputData

OutputData

ObjectOutput

ObjectInput


Patrick Healy

Class #15 – Input and Output Character Stream Classes (Character = 2 bytes)

Reader

Writer

StreamTokenizer

Object

PrintWriter

BufferedWriter

CharArrayWriter

PipedWriter

FilterWriter

PipedReader

LineNumberReader

FileReader

PushBackReader

FileWriter

StringWriter

StringReader

InputStreamReader

CharArrayReader

BufferedReader

FilterReader

OutputStreamWriter

How is I/O Handled in Java?A File object encapsulates the properties of a file or a path, but does not contain the methods for reading/writing data from/to a file. In order to perform I/O, you need to create objects using appropriate Java I/O classes.

Formatter output = new Formatter("temp.txt");

output.format("%s", "Java 101");

output.close();

Scanner input = new Scanner(new File("temp.txt"));

System.out.println(input.nextLine());

Program

Input object created from an

input class

Output object created from an

output class

Input stream

Output stream

File

File 01011…1001

11001…1011

Text Files vs. Binary Files Data stored in a text file are represented in human-readable form. Data

stored in a binary file are represented in binary form. You cannot read binary files. Binary files are designed to be read by programs. For example, the Java source programs are stored in text files and can be read by a text editor, but the Java classes are stored in binary files and are read by the JVM. The advantage of binary files is that they are more efficient to process than text files.

Although it is not technically precise and correct, you can imagine that a text file consists of a sequence of characters and a binary file consists of a sequence of bits. For example, the decimal integer 199 is stored as the sequence of three characters: '1', '9', '9' in a text file and the same integer is stored as a byte-type value C7 in a binary file, because decimal 199 equals to hex C7.

Binary I/OText I/O requires encoding and decoding. The JVM converts a Unicode to a file specific encoding when writing a character and coverts a file specific encoding to a Unicode when reading a character. Binary I/O does not require conversions. When you write a byte to a file, the original byte is copied into the file. When you read a byte from a file, the exact byte in the file is returned.

Text I/O program

The Unicode of the character

Encoding/ Decoding

Binary I/O program

A byte is read/written (b)

(a)

e.g.,

"199"

The encoding of the character is stored in the file

0x31

e.g.,

199 00110111

00110001 00111001 00111001

0x39 0x39

0xC7

The same byte in the file

Binary I/O Classes

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

java.io.InputStream

+read(): int

+read(b: byte[]): int

+read(b: byte[], off: int, len: int): int

+available(): int

+close(): void

+skip(n: long): long

+markSupported(): boolean

+mark(readlimit: int): void

+reset(): void

Reads the next byte of data from the input stream. The value byte is returned as an int value in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value –1 is returned.

Reads up to b.length bytes into array b from the input stream and returns the actual number of bytes read. Returns -1 at the end of the stream.

Reads bytes from the input stream and stores into b[off], b[off+1], …, b[off+len-1]. The actual number of bytes read is returned. Returns -1 at the end of the stream.

Returns the number of bytes that can be read from the input stream.

Closes this input stream and releases any system resources associated with the stream.

Skips over and discards n bytes of data from this input stream. The actual number of bytes skipped is returned.

Tests if this input stream supports the mark and reset methods.

Marks the current position in this input stream.

Repositions this stream to the position at the time the mark method was last called on this input stream.

The value returned is a byte as an int type.

InputStream

The value is a byte as an int type.

OutputStream

java.io.OutputStream

+write(int b): void

+write(b: byte[]): void

+write(b: byte[], off: int, len: int): void

+close(): void

+flush(): void

Writes the specified byte to this output stream. The parameter b is an int value. (byte)b is written to the output stream.

Writes all the bytes in array b to the output stream.

Writes b[off], b[off+1], …, b[off+len-1] into the output stream.


Flushes this output stream and forces any buffered output bytes to be written out.

FileInputStream/FileOutputStream

FileInputStream/FileOutputStream associates a binary input/output stream with an external file. All the methods in FileInputStream/FileOuptputStream are inherited from its superclasses.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

FileInputStreamTo construct a FileInputStream, use the following constructors:

public FileInputStream(String filename)

public FileInputStream(File file)

A java.io.FileNotFoundException would occur if you attempt to create a FileInputStream with a nonexistent file.

FileOutputStreamTo construct a FileOutputStream, use the following constructors:

public FileOutputStream(String filename)public FileOutputStream(File file)public FileOutputStream(String filename, boolean append)public FileOutputStream(File file, boolean append)

If the file does not exist, a new file would be created. If the file already exists, the first two constructors would delete the current contents in the file. To retain the current content and append new data into the file, use the last two constructors by passing true to the append parameter.

TestFileStreamTestFileStream RunRun

FilterInputStream/FilterOutputStream

Filter streams are streams that filter bytes for some purpose. The basic byte input stream provides a read method that can only be used for reading bytes. If you want to read integers, doubles, or strings, you need a filter class to wrap the byte input stream. Using a filter class enables you to read integers, doubles, and strings instead of bytes and characters. FilterInputStream and FilterOutputStream are the base classes for filtering data. When you need to process primitive numeric types, use DatInputStream and DataOutputStream to filter bytes.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

DataInputStream/DataOutputStreamDataInputStream reads bytes from the stream and converts them into appropriate primitive type values or strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

DataOutputStream converts primitive type values or strings into bytes and output the bytes to the stream.

DataInputStream

DataInputStream extends FilterInputStream and implements the DataInput interface.

java.io.DataInput

+readBoolean(): boolean

+readByte(): byte

+readChar(): char

+readFloat(): float

+readDouble(): float

+readInt(): int

+readLong(): long

+readShort(): short

+readLine(): String

+readUTF(): String

Reads a Boolean from the input stream.

Reads a byte from the input stream.

Reads a character from the input stream.

Reads a float from the input stream.

Reads a double from the input stream.

Reads an int from the input stream.

Reads a long from the input stream.

Reads a short from the input stream.

Reads a line of characters from input.

Reads a string in UTF format.

InputStream

FilterInputStream

DataInputStream

+DataInputStream( in: InputStream)

DataOutputStreamDataOutputStream extends FilterOutputStream and implements the DataOutput interface.

java.io.DataOutput

+writeBoolean(b: Boolean): void

+writeByte(v: int): void

+writeBytes(s: String): void

+writeChar(c: char): void

+writeChars(s: String): void

+writeFloat(v: float): void

+writeDouble(v: float): void

+writeInt(v: int): void

+writeLong(v: long): void

+writeShort(v: short): void

+writeUTF(s: String): void

Writes a Boolean to the output stream.

Writes to the output stream the eight low-order bits of the argument v.

Writes the lower byte of the characters in a string to the output stream.

Writes a character (composed of two bytes) to the output stream.

Writes every character in the string s, to the output stream, in order, two bytes per character.

Writes a float value to the output stream.

Writes a double value to the output stream.

Writes an int value to the output stream.

Writes a long value to the output stream.

Writes a short value to the output stream.

Writes two bytes of length information to the output stream, followed by the UTF representation of every character in the string s.

OutputStream

FilterOutputStream

DataOutputStream

+DataOutputStream( out: OutputStream)

Characters and Strings in Binary I/O A Unicode consists of two bytes. The writeChar(char c) method writes the Unicode of character c to the output. The writeChars(String s) method writes the Unicode for each character in the string s to the output.

Why UTF-8? What is UTF-8?

UTF-8 is a coding scheme that allows systems to operate with both ASCII and Unicode efficiently. Most operating systems use ASCII. Java uses Unicode. The ASCII character set is a subset of the Unicode character set. Since most applications need only the ASCII character set, it is a waste to represent an 8-bit ASCII character as a 16-bit Unicode character. The UTF-8 is an alternative scheme that stores a character using 1, 2, or 3 bytes. ASCII values (less than 0x7F) are coded in one byte. Unicode values less than 0x7FF are coded in two bytes. Other Unicode values are coded in three bytes.

Using DataInputStream/DataOutputStream

Data streams are used as wrappers on existing input and output streams to filter data in the original stream. They are created using the following constructors:

public DataInputStream(InputStream instream)public DataOutputStream(OutputStream outstream)

The statements given below create data streams. The first statement creates an input stream for file in.dat; the second statement creates an output stream for file out.dat.

DataInputStream infile = new DataInputStream(new FileInputStream("in.dat"));DataOutputStream outfile = new DataOutputStream(new FileOutputStream("out.dat"));

TestDataStreamTestDataStream RunRun

Checking End of File

TIP: If you keep reading data at the end of a stream, an EOFException would occur. So how do you check the end of a file? You can use input.available() to check it. input.available() == 0 indicates that it is the end of a file.

Order and Format

CAUTION: You have to read the data in the same order and same format in which they are stored. For example, since names are written in UTF-8 using writeUTF, you must read names using readUTF.

BufferedInputStream/BufferedOutputStream

Using buffers to speed up I/O

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

BufferedInputStream/BufferedOutputStream does not contain new methods. All the methods BufferedInputStream/BufferedOutputStream are inherited from the InputStream/OutputStream classes.

Constructing BufferedInputStream/BufferedOutputStream

// Create a BufferedInputStream

public BufferedInputStream(InputStream in)

public BufferedInputStream(InputStream in, int bufferSize)

// Create a BufferedOutputStream

public BufferedOutputStream(OutputStream out)

public BufferedOutputStream(OutputStreamr out, int bufferSize)

Case Studies: Copy File This case study develops a program that copies files. The user needs to provide a source file and a target file as command-line arguments using the following command:

java Copy source target

The program copies a source file to a target file and displays the number of bytes in the file. If the source does not exist, tell the user the file is not found. If the target file already exists, tell the user the file already exists.

CopyCopy RunRun

Object I/O

DataInputStream/DataOutputStream enables you to perform I/O for primitive type values and strings. ObjectInputStream/ObjectOutputStream enables you to perform I/O for objects in addition for primitive type values and strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

Optional

ObjectInputStream

ObjectInputStream extends InputStream and implements ObjectInput and ObjectStreamConstants.

java.io.ObjectInput

+readObject(): Object

Reads an object.

java.io.InputStream

java.io.ObjectInputStream

+ObjectInputStream(in: InputStream)

java.io.DataInput

ObjectStreamConstants

ObjectOutputStream

ObjectOutputStream extends OutputStream and implements ObjectOutput and ObjectStreamConstants.

java.io.ObjectOutput

+writeObject(o: Object): void

Writes an object.


java.io.ObjectOutputStream

+ObjectOutputStream(out: OutputStream)

java.io.DataOutput


Using Object StreamsYou may wrap an ObjectInputStream/ObjectOutputStream on any InputStream/OutputStream using the following constructors:

// Create an ObjectInputStream

public ObjectInputStream(InputStream in)

// Create an ObjectOutputStream

public ObjectOutputStream(OutputStream out)

TestObjectOutputStreamTestObjectOutputStream RunRun

TestObjectInputStreamTestObjectInputStream RunRun

Random Access Files

All of the streams you have used so far are known as read-only or write-only streams. The external files of these streams are sequential files that cannot be updated without creating a new file. It is often necessary to modify files or to insert new records into files. Java provides the RandomAccessFile class to allow a file to be read from and write to at random locations.

RandomAccessFile

Creates a RandomAccessFile stream with the specified File object and mode.

Creates a RandomAccessFile stream with the specified file name string and mode.

Closes the stream and releases the resource associated with the stream.

Returns the offset, in bytes, from the beginning of the file to where the next read or write occurs.

Returns the length of this file.

Reads a byte of data from this file and returns –1 an the end of stream.

Reads up to b.length bytes of data from this file into an array of bytes.

Reads up to len bytes of data from this file into an array of bytes.

Sets the offset (in bytes specified in pos) from the beginning of the stream to where the next read or write occurs.

Sets a new length of this file.

Skips over n bytes of input discarding the skipped bytes.

Writes b.length bytes from the specified byte array to this file, starting at the current file pointer.

Writes len bytes from the specified byte array starting at offset off to this file.

DataInput

DataInput

java.io.RandomAccessFile

+RandomAccessFile(file: File, mode: String)

+RandomAccessFile(name: String, mode: String)

+close(): void

+getFilePointer(): long

+length(): long

+read(): int


+read(b: byte[], off: int, len: int) : int

+seek(long pos): void

+setLength(newLength: long): void

+skipBytes(int n): int


+write(byte b[], int off, int len) +write(b: byte[], off: int, len: int):

void

File PointerA random access file consists of a sequence of bytes. There is a special marker called file pointer that is positioned at one of these bytes. A read or write operation takes place at the location of the file pointer. When a file is opened, the file pointer sets at the beginning of the file. When you read or write data to the file, the file pointer moves forward to the next data. For example, if you read an int value using readInt(), the JVM reads four bytes from the file pointer and now the file pointer is four bytes ahead of the previous location.

byte

file

byte

…

byte

byte

byte

byte

byte

…

byte

byte

byte

byte

byte

file pointer

byte

file

byte

…

byte

byte

byte

byte

byte

…

byte

byte

byte

byte

byte

file pointer

(A) Before readInt()

(B) Before readInt()

RandomAccessFile MethodsMany methods in RandomAccessFile are the same as those in DataInputStream and DataOutputStream. For example, readInt(), readLong(), writeDouble(), readLine(), writeInt(), and writeLong() can be used in data input stream or data output stream as well as in RandomAccessFile streams.

RandomAccessFile Methods, cont.

void seek(long pos) throws IOException;Sets the offset from the beginning of the RandomAccessFile stream to where the next reador write occurs.

long getFilePointer() IOException;Returns the current offset, in bytes, from thebeginning of the file to where the next reador write occurs.


long length()IOExceptionReturns the length of the file.

final void writeChar(int v) throws IOExceptionWrites a character to the file as a two-byte Unicode, with the high byte written first.

final void writeChars(String s)throws IOExceptionWrites a string to the file as a sequence ofcharacters.

RandomAccessFile Constructor

RandomAccessFile raf =new RandomAccessFile("test.dat", "rw"); //allows read and write

RandomAccessFile raf =new RandomAccessFile("test.dat", "r"); //read only

Case Studies: Address BookOptional

Now let us use RandomAccessFile to create a useful project for storing and viewing and address book. The user interface of the program is shown in Figure 16.24. The Add button stores a new address to the end of the file. The First, Next, Previous, and Last buttons retrieve the first, next, previous, and last addresses from the file, respectively.

Fixed Length String I/O

Random access files are often used to process files of records. For convenience, fixed-length records are used in random access files so that a record can be located easily. A record consists of a fixed number of fields. A field can be a string or a primitive data type. A string in a fixed-length record has a maximum size. If a string is smaller than the maximum size, the rest of the string is padded with blanks.

Record 1

Record 2

Record n

Field1 Field 2 … Field k

file e.g.,

Student 1

Student 2

Student n

name street city state zip

FixedLengthStringIOFixedLengthStringIO

End of PresentationEnd of Presentation

Binary Input & Output Binary Input & Output Chapter 18 Chapter 18


Patrick Healy

Class #15 – Input and Output How is I/O Handled in Java?

A File object encapsulates the properties of a file or a path, but does not contain the methods for reading/writing data from/to a file. In order to perform I/O, you need to create objects using appropriate Java I/O classes.

Formatter output = new Formatter(“outfile.txt");

output.format("%s", "Java 120"); // Write a string to outfile.txt

output.close(); // Close the output file outfile.txt

Scanner input = new Scanner(new File("temp.txt")); // Create object

System.out.println(input.nextLine()); // Read a line

Program


input class


output class

Input stream

Output stream

File

File 01011…1001

11001…1011


Patrick Healy

Class #15 – Input and Output Text Files vs. Binary Files

Data stored in a text file are represented in human-readable form. Data stored in a binary file are represented in binary form. You cannot read binary files. Binary files are designed to be read by programs. For example, the Java source programs are stored in text files and can be read by a text editor, but the Java classes are stored in binary files and are read by the JVM. The advantage of binary files is that they are more efficient to process than text files.

Although it is not technically precise and correct, you can imagine that a text file consists of a sequence of characters and a binary file consists of a sequence of bits. For example, the decimal integer 199 is stored as the sequence of three characters: '1', '9', '9' in a text file and the same integer is stored as a byte-type value C7 in a binary file ( Note: decimal 199 equals to Hex C7.)


Patrick Healy

Class #15 – Input and Output Binary File I/O

Text I/O requires encoding and decoding. The JVM converts a Unicode char to a file-specific encoding when writing a character and coverts a file-specific encoding to a Unicode char when reading a character. Binary I/O does not require conversions. When you write a byte to a file, the original byte is copied into the file. When you read a byte from a file, the exact byte in the file is returned.

Text I/O program


Encoding/ Decoding

Binary I/O program


(a)

e.g.,

"199"


0x31

e.g.,

199 00110111

00110001 00111001 00111001

0x39 0x39

0xC7



Patrick Healy

Class #15 – Input and Output Binary I/O Classes Inheritance Hierarchy

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


Patrick Healy


java.io.InputStream

+read(): int


+read(b: byte[], off: int, len: int): int

+available(): int

+close(): void

+skip(n: long): long

+markSupported(): boolean

+mark(readlimit: int): void

+reset(): void

Reads the next byte of data from the input stream. The value byte is returned as an int value in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value –1 is returned.

Reads up to b.length bytes into array b from the input stream and returns the actual number of bytes read. Returns -1 at the end of the stream.

Reads bytes from the input stream and stores into b[off], b[off+1], …, b[off+len-1]. The actual number of bytes read is returned. Returns -1 at the end of the stream.

Returns the number of bytes that can be read from the input stream.


Skips over and discards n bytes of data from this input stream. The actual number of bytes skipped is returned.

Tests if this input stream supports the mark and reset methods.

Marks the current position in this input stream.

Repositions this stream to the position at the time the mark method was last called on this input stream.

The value returned is a byte as an int type.

InputStream (a byte stream class)


Patrick Healy


The value is a byte as an int type.

OutputStream ( a byte stream class)


+write(int b): void


+write(b: byte[], off: int, len: int): void

+close(): void

+flush(): void

Writes the specified byte to this output stream. The parameter b is an int value. (byte)b is written to the output stream.

Writes all the bytes in array b to the output stream.

Writes b[off], b[off+1], …, b[off+len-1] into the output stream.


Flushes this output stream and forces any buffered output bytes to be written out.


Patrick Healy


FileInputStream & FileOutputStream (byte streams)

FileInputStream/FileOutputStream associates a binary input/output stream with an external file. All the methods in FileInputStream/FileOuptputStream are inherited from its superclasses.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


Patrick Healy


FileInputStream (byte stream)

To construct a FileInputStream, use the following constructors:

public FileInputStream(String filename)

public FileInputStream(File file)

A java.io.FileNotFoundException would occur if you attempt to create a FileInputStream with a nonexistent file.


Patrick Healy

Class #15 – Input and Output FileOutputStream (byte stream)

To construct a FileOutputStream, use the following constructors:public FileOutputStream(String filename)public FileOutputStream(File file)public FileOutputStream(String filename, boolean append)public FileOutputStream(File file, boolean append) // append = true to add on to the file

If the file does not exist, a new file would be created. If the file already exists, the first two constructors would delete the current contents in the file. To retain the current content and append new data into the file, use the last two constructors by passing true to the append parameter.Demo Program: TestFileStream.java


Patrick Healy


FilterInputStream/FilterOutputStream

Filter streams are streams that filter bytes for some purpose. The basic byte input stream provides a read method that can only be used for reading bytes. If you want to read integers, doubles, or strings, you need a filter class to wrap the byte input stream. Using a filter class enables you to read integers, doubles, and strings instead of bytes and characters. FilterInputStream and FilterOutputStream are the base classes for filtering data. When you need to process primitive numeric types, use DataInputStream and DataOutputStream to filter bytes.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


Patrick Healy


DataInputStream & DataOutputStream (byte streams)DataInputStream reads bytes from the stream and converts them into appropriate primitive type values or strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

DataOutputStream converts primitive type values or strings into bytes and outputs the bytes to the stream.


Patrick Healy


DataInputStream ( byte stream)

DataInputStream extends FilterInputStream and implements the DataInput interface.

java.io.DataInput

+readBoolean(): boolean

+readByte(): byte

+readChar(): char

+readFloat(): float

+readDouble(): float

+readInt(): int

+readLong(): long

+readShort(): short

+readLine(): String

+readUTF(): String

Reads a Boolean from the input stream.

Reads a byte from the input stream.

Reads a character from the input stream.

Reads a float from the input stream.

Reads a double from the input stream.

Reads an int from the input stream.

Reads a long from the input stream.

Reads a short from the input stream.

Reads a line of characters from input.

Reads a string in UTF format.

InputStream

FilterInputStream

DataInputStream

+DataInputStream( in: InputStream)


Patrick Healy


DataOutputStream (byte stream)DataOutputStream extends FilterOutputStream and implements the DataOutput interface.

java.io.DataOutput

+writeBoolean(b: Boolean): void

+writeByte(v: int): void

+writeBytes(s: String): void

+writeChar(c: char): void

+writeChars(s: String): void

+writeFloat(v: float): void

+writeDouble(v: float): void

+writeInt(v: int): void

+writeLong(v: long): void

+writeShort(v: short): void

+writeUTF(s: String): void

Writes a Boolean to the output stream.

Writes to the output stream the eight low-order bits of the argument v.

Writes the lower byte of the characters in a string to the output stream.

Writes a character (composed of two bytes) to the output stream.

Writes every character in the string s, to the output stream, in order, two bytes per character.

Writes a float value to the output stream.

Writes a double value to the output stream.

Writes an int value to the output stream.

Writes a long value to the output stream.

Writes a short value to the output stream.

Writes two bytes of length information to the output stream, followed by the UTF representation of every character in the string s.

OutputStream

FilterOutputStream

DataOutputStream

+DataOutputStream( out: OutputStream)


Patrick Healy

Class #15 – Input and Output Characters and Strings in Binary I/O

A Unicode char is 2 bytes. The writeChar(char ch) method writes the Unicode of character ch to the output. The writeChars(String str) method writes the Unicode for each character in the string str to the output file.

What is UTF-8 ? Why use UTF-8 ? [ UTF means Unicode Text File ]

UTF-8 is a coding scheme that allows systems to operate with both ASCII and Unicode efficiently. Most operating systems use ASCII. Java uses Unicode. The ASCII character set is a subset of the Unicode character set. Since most applications need only the ASCII character set, it is a waste to represent an 8-bit ASCII character as a 16-bit Unicode character. The UTF-8 is an alternative scheme that stores a character using 1, 2, or 3 bytes. ASCII values (less than 0x7F) (127 decimal) are coded in one byte. Unicode values less than 0x7FF are coded in two bytes. Other Unicode values are coded in three bytes.


Patrick Healy


Using DataInputStream/DataOutputStream

Data streams are used as wrappers on existing input and output streams to filter data in the original stream. They are created using the following constructors:

public DataInputStream(InputStream instream)

public DataOutputStream(OutputStream outstream)

The statements below create data streams. The first statement creates an input stream for file in.dat; the second statement creates an output stream for file out.dat.

DataInputStream infile = new DataInputStream(new FileInputStream("in.dat"));DataOutputStream outfile = new DataOutputStream(new FileOutputStream("out.dat"));Demo Program: TestDataStream.java


Patrick Healy


Checking for the End of File (EOF)

TIP: If the program tried to read data at the end of a stream, an EOFException would occur. How do you check the end of a file? Use input.available() to check for EOF. if input.available() == 0 then the program is at the end of a file. (EOF)

Order and Format

CAUTION: You have to read the data in the same order and same format in which they are stored. For example, if names are written in UTF-8 using writeUTF (String str), you MUST read the names using the readUTF method.


Patrick Healy


BufferedInputStream/BufferedOutputStream Use buffers to speed up I/O processes

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

BufferedInputStream/BufferedOutputStream does not contain new methods. All the methods BufferedInputStream/BufferedOutputStream are inherited from the InputStream/OutputStream classes.


Patrick Healy


Constructing BufferedInputStream/BufferedOutputStream

// Create a BufferedInputStreampublic BufferedInputStream(InputStream in)public BufferedInputStream(InputStream in, int bufferSize) // Create a BufferedOutputStream

public BufferedOutputStream(OutputStream out)

public BufferedOutputStream(OutputStream out, int bufferSize)


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CopyFile.java

CopyFile.java is a program that copies files. The user needs to provide a source file and a target file as command-line arguments using the following command:

java CopyFile source target

Also: java CompFile source target

The program copies a source file to a target file and displays the number of bytes in the file. If the source does not exist, tell the user the file is not found. If the target file already exists, tell the user the file already exists.


Patrick Healy


Object I/O (optional)

DataInputStream/DataOutputStream enables you to perform I/O for primitive type values and strings. ObjectInputStream/ObjectOutputStream enables you to perform I/O for objects in addition for primitive type values and strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


Patrick Healy


ObjectInputStream (optional)

ObjectInputStream extends InputStream and implements ObjectInput and ObjectStreamConstants.

java.io.ObjectInput

+readObject(): Object

Reads an object.

java.io.InputStream

java.io.ObjectInputStream

+ObjectInputStream(in: InputStream)

java.io.DataInput



Patrick Healy


ObjectOutputStream (optional)

ObjectOutputStream extends OutputStream and implements ObjectOutput and ObjectStreamConstants.

java.io.ObjectOutput

+writeObject(o: Object): void

Writes an object.


java.io.ObjectOutputStream

+ObjectOutputStream(out: OutputStream)

java.io.DataOutput



Patrick Healy


Using Object Streams (optional)

You may wrap an ObjectInputStream/ObjectOutputStream on any InputStream/OutputStream using the following constructors:

// Create an ObjectInputStreampublic ObjectInputStream(InputStream in) // Create an ObjectOutputStreampublic ObjectOutputStream(OutputStream out)

Demo: TestObjectOutputStream.java

TestObjectInputStream.java


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The Serializable Interface

Not all objects can be written to an output stream. Objects that CAN be written to an object stream is said to be serializable. A serializable object is an instance of the java.io.Serializable interface. So the class of a serializable object must implement the Serializable interface.

The Serializable interface is a marker interface. It has no methods, so you don't need to add additional code in your class that implements Serializable.

Implementing this interface enables the Java serialization mechanism to automate the process of storing the objects and arrays.


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The transient Keyword

If an object is an instance of Serializable, but it contains non-serializable instance data fields, can the object be serialized? The answer is NO !

To enable the object to be serialized, you can use the transient keyword to mark these data fields to tell the JVM to ignore these fields when writing the object to an object stream.


Patrick Healy

Class #15 – Input and Output The transient Keyword, cont.

Consider the following class:

public class ITP120 implements java.io.Serializable {

private int v1;

private static double v2;

private transient A v3 = new A();

}

class A { } // A is not serializable

When an object of the ITP120 class is serialized, only variable v1 is serialized. Variable v2 is not serialized because it is a static variable, and variable v3 is not serialized because it is marked transient. If v3 were not marked transient, a java.io.NotSerializableException would occur.


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Serializing Arrays (optional)

An array is serializable if all its elements are serializable. So an entire array can be saved using writeObject into a file and later restored using readObject.

Listing 18.6 stores an array of five int values, an array of three strings, and an array of two JButton objects, and reads them back to display on the console.

Demo Program: TestObjectStreamForArray.java


Patrick Healy


Random Access Files

All of the streams you have used so far are known as read-only or write-only streams. The external files of these streams are sequential files that cannot be updated without creating a new file.

It is often necessary to modify files or to insert new records into files. Java provides the RandomAccessFile class to allow a file to be read from and write to at random locations.


Patrick Healy

Class #15 – Input and Output RandomAccessFile

Creates a RandomAccessFile stream with the specified File object and mode.

Creates a RandomAccessFile stream with the specified file name string and mode.

Closes the stream and releases the resource associated with the stream.


Returns the length of this file.

Reads a byte of data from this file and returns –1 an the end of stream.

Reads up to b.length bytes of data from this file into an array of bytes.

Reads up to len bytes of data from this file into an array of bytes.

Sets the offset (in bytes specified in pos) from the beginning of the stream to where the next read or write occurs.

Sets a new length of this file.

Skips over n bytes of input discarding the skipped bytes.

Writes b.length bytes from the specified byte array to this file, starting at the current file pointer.

Writes len bytes from the specified byte array starting at offset off to this file.

DataInput

DataInput

java.io.RandomAccessFile

+RandomAccessFile(file: File, mode: String)

+RandomAccessFile(name: String, mode: String)

+close(): void

+getFilePointer(): long

+length(): long

+read(): int


+read(b: byte[], off: int, len: int) : int

+seek(long pos): void

+setLength(newLength: long): void

+skipBytes(int n): int


+write(byte b[], int off, int len) +write(b: byte[], off: int, len: int):

void


Patrick Healy

Class #15 – Input and Output File Pointers

A random access file consists of a sequence of bytes. There is a special marker called file pointer that is positioned at one of these bytes. A read or write operation takes place at the location of the file pointer. When a file is opened, the file pointer sets at the beginning of the file. When you read or write data to the file, the file pointer moves forward to the next data. For example, if you read an int value using readInt(), the JVM reads four bytes from the file pointer and now the file pointer is four bytes ahead of the previous location.


Patrick Healy

Class #15 – Input and Output File Pointers

(moving the pointer 4 bytes ahead)

byte

file

byte

…

byte

byte

byte

byte

byte

…

byte

byte

byte

byte

byte

file pointer

byte

file

byte

…

byte

byte

byte

byte

byte

…

byte

byte

byte

byte

byte

file pointer

(A) Before readInt()

(B) Before readInt()


Patrick Healy


RandomAccessFile Methods

Many methods in RandomAccessFile are the same as those in

DataInputStream and DataOutputStream.

For example, readInt(), readLong(), writeDouble(), readLine(), writeInt(), and writeLong()

can be used in data input stream or data output stream as well as in RandomAccessFile streams.


Patrick Healy

Class #15 – Input and Output RandomAccessFile Methods, cont.

void seek(long pos) throws IOException;

Sets the offset from the beginning of the RandomAccessFile stream to where the next reador write occurs.

long getFilePointer() IOException;

Returns the current offset, in bytes, from thebeginning of the file to where the next reador write occurs.


Patrick Healy



long length()IOExceptionReturns the length of the file.

final void writeChar(int v) throws IOExceptionWrites a character to the file as a two-byte Unicode, with the high byte written first.

final void writeChars(String s)throws IOExceptionWrites a string to the file as a sequence ofcharacters.


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RandomAccessFile Constructors

RandomAccessFile raf =new RandomAccessFile("test.dat", "rw"); //allows read and write to the file

RandomAccessFile raf =new RandomAccessFile("test.dat", "r"); //read only

Demo program: TestRandomAccessFile.java

(uses FixedLengthStringIO.java)

Case Study: Address BookNow let us use RandomAccessFile to create a useful project for storing and viewing and address book. The user interface of the program is shown in Figure 16.24. The Add button stores a new address to the end of the file. The First, Next, Previous, and Last buttons retrieve the first, next, previous, and last addresses from the file, respectively.

Run: AddressBook.java which uses FixedLengthStringIO.java

Fixed Length String I/O

Random access files are often used to process files of records. For convenience, fixed-length records are used in random access files so that a record can be located easily. A record consists of a fixed number of fields. A field can be a string or a primitive data type. A string in a fixed-length record has a maximum size. If a string is smaller than the maximum size, the rest of the string is padded with blanks.

Record 1

Record 2

Record n

Field1 Field 2 … Field k

file e.g.,

Student 1

Student 2

Student n

name street city state zip

FixedLengthStringIOFixedLengthStringIO

78

Chapter 18 Demo Programs

ReadBytes.java (skip) WriteData.java

WriteDemo.java ReadData.java

ShowFile.java

CopyFile.java CopyFileUsingByteStream.java

CompFile.java

RWData.java

RandomAccessDemo.java

PrintWriterDemo.java

ReadChars.java or BuffReader.java

ReadLines.java (BufferedReader)

79


TextFileScannerDemo.java Uses input file morestuff.txt

HasNextLineDemo.java Uses input file original.txt and creates output file numbered.txt

BufferReaderDemo.java Uses input file: buffer.txt

80


TestDataStreams.java

TestFileClass.java

TestPrintWriters.java

ViewFile.java (GUI text file viewer program)

needs MyFrameWithExitHanding.java class file

ParsingTextFile.java (needs grades.dat file)

(creates gradesout.dat)

TestRandomAccessFile.java AddressBook.java (creates file address.dat)

needs FixedLengthStringIO.class file

81


TestDataStream.java

TestFileReader.java (needs temp.txt)

TestFileStream.java

TestFileWriter.java (needs testdata.txt)

TestObjectStreamForArray.java ( creates array.dat)

TestObjectOutputStream.java

(creates object.dat)

TestObjectInputStream.java (reads object.dat)


Patrick Healy

Class #15 – Input and Output Chapter 18 Input / Output

Optional: More on Java File I/O Optional: More on Java File I/O Chapter 18 Java I ITP 120 Chapter 18 Java I ITP 120


Patrick Healy

Class #15 – Input and Output Chapter 18: More on Input and Output

Stream Classes (byte & character streams)Predefined Streams (System.in, System.out, System.err)Processing External FilesData StreamsPrint StreamsBuffered StreamsText Input and Output on the ConsoleRandom Access Files


Patrick Healy

Class #15 – Input and Output Chapter 18 Input /Output Objectives Understand input & output streams and learn how to create them. Discover the uses of byte and character streams. To know how to read from / write to external files using file streams. To become familiar with the File class. To use print streams to output data of primitive types in text format. To know how to read and write text data files. Use text input and output on the console. Use RandomAccessFile for reading & writing random access files.


Patrick Healy

Class #15 – Input and Output Overview The java.io.* package provides a library of classes to read and write

various types of data. In Java, all data I/O is handled in the form of streams Data streams can be byte streams or character streams The java.io package has classes that process byte streams of all types NOTE: In Java, a character is 2 BYTES ! NOTE: Unicode character is 2 bytes ! The Reader and Writer classes process character streams. Streams can be layered, so that one type of streams can be converted

to another type of streams by chaining. Chaining a character stream reader to a byte stream reader to read bytes on one end and produce characters at the other end .


Patrick Healy

Class #15 – Input and Output Overview Streams In Java, all Input/Output is handled by streams A stream is an abstraction of the continuous one-way flow of data Java streams can be applied to any source of data, so it is easy to get

input from the keyboard and send output to a monitor, and the same applies to file input & output.

All streams EXCEPT random-access file streams flow only in one direction.

See the diagram on the next slide


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Overview --- Streams

A stream is an abstraction of a continuous one-way flow of data.

Program

Output Stream

File

Input Stream


Patrick Healy

Class #15 – Input and Output Overview and Background The original version of Java defined only the byte stream, but character

streams were quickly added. Byte streams can be used when reading or writing binary data. Character streams are designed for handling character I/O. Character streams use UNICODE. In Java, a character is 2 bytes Unicode is for the internationalization of Java in different languages. The Java I/O system is quite LARGE because of the TWO separate

class hierarchies of bytes and streams.

How is I/O Handled in Java?A File object encapsulates the properties of a file or a path, but does not contain the methods for reading/writing data from/to a file. In order to perform I/O, you need to create objects using appropriate Java I/O classes.

Formatter output = new Formatter("temp.txt");

output.format("%s", "Java ITP 120");

output.close();

Scanner input = new Scanner(new File("temp.txt"));

System.out.println(input.nextLine());

Program


input class


output class

Input stream

Output stream

File

File 01011…1001

11001…1011


Patrick Healy

Class #15 – Input and Output Text Files vs. Binary Files

Data stored in a text file are represented in human-readable form. Data stored in a binary file are represented in binary form. You cannot read binary files. Binary files are designed to be read by programs. For example, the Java source programs are stored in text files and can be read by a text editor, but the Java classes are stored in binary files and are read by the JVM.

The advantage of binary files is that they are more efficient to process than text files.

Although it is not technically precise and correct, you can imagine that a text file consists of a sequence of characters and a binary file consists of a sequence of bits. For example, the decimal integer 199 is stored as the sequence of three characters: '1', '9', '9' in a text file and the same integer is stored as a byte-type value C7 in a binary file, because decimal 199 equals to hex C7 ( 12 x 16 + 7 = 192 + 7 = 199 decimal )

Binary I/OText I/O requires encoding and decoding. The JVM converts a Unicode character to file-specific encoding when writing a character, and coverts a file-specific encoding to a Unicode character when reading a character. Binary I/O does not require conversions. When you write a byte to a file, the original byte is copied into the file. When you read a byte from a file, the exact byte in the file is returned.

Text I/O program


Encoding/ Decoding

Binary I/O program


(a)

e.g.,

"199"


0x31

e.g.,

199 00110111

00110001 00111001 00111001

0x39 0x39

0xC7



Patrick Healy


2 Types of Stream Classes: Bytes & Characters

The stream classes can be categorized into two types: byte streams and character streams.

The InputStream/OutputStream class is theroot of all byte stream classes

The Reader/Writer class is the root of all character streamclasses.

The subclasses of InputStream/OutputStream are analogous to the subclasses of Reader/Writer.


Patrick Healy


Byte Stream Classes (note: “stream” )

InputStream

OutputStream

RandomAccessFile

Object

PipeOutputStream

SequenceInputStream

StringBufferInputStream

ByteArrayOutputStream

ObjectOutputStream

FilterOutputStream

FileOutputStream

PipedInputStream

PushBackInputStream

BufferedInputStream

LineNumberInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

ByteArrayInputStream InputData

OutputData

ObjectOutput

ObjectInput


Patrick Healy

Class #15 – Input and Output Character Stream Classes (Character = 2 bytes)

Reader

Writer

StreamTokenizer

Object

PrintWriter

BufferedWriter

CharArrayWriter

PipedWriter

FilterWriter

PipedReader

LineNumberReader

FileReader

PushBackReader

FileWriter

StringWriter

StringReader

InputStreamReader

CharArrayReader

BufferedReader

FilterReader

OutputStreamWriter


Patrick Healy

Class #15 – Input and Output Predefined Streams in Java All Java programs automatically import the java.lang package.

The java.lang package defines a class called System which encapsulates several aspects of the runtime environment.

The System class contains 3 predefined stream variables called:

in, out, and err (System.in, System.out, System.err)

These variables are declared as public and static with the System class. This means they can be used by any other part of your program and without a reference to a specific object in the System class.


Patrick Healy

Class #15 – Input and Output Predefined Streams in Java: System class

System.in refers to the standard input stream which is the keyboard by default. (Keyboard )

System.out refers to the standard output stream which is the console by default. (Monitor)

System.err refers to the standard error stream which is also the console by default. (Monitor)

These streams may be redirected to any compatible I/O device.


Patrick Healy

Class #15 – Input and Output Predefined Streams in Java: System class System.in is an object of type InputStream. (byte stream)

System.out is an object of type PrintStream. (byte stream)

System.err is an object of type PrintStream. (byte stream)

They are all byte streams and are a part of the original Java specification.

They are NOT character streams ! (Unicode character = 2 bytes)


Patrick Healy

Class #15 – Input and Output Reading Keyboard Input// Read an array of bytes from the keyboard.

import java.io.*;

public class ReadBytes {

public static void main(String[ ] args)

throws IOException {

byte data[ ] = new byte[10]; // Byte array “data” holds 10 bytes

System.out.println("Enter some characters:");

System.in.read(data); // Use the “read” method to read some bytes

System.out.print("You entered: ");

for(int i=0; i < data.length; i++)

System.out.print((char) data[i]); // Cast data to a character

} // End main method

} // End class ReadBytes


Patrick Healy

Class #15 – Input and Output Reading Keyboard Input Here is a sample run from the previous program:

Enter some characters: (prompt from program)

READ BYTES (User entered READ BYTES)

You entered: READ BYTES (output from program)


Patrick Healy

Class #15 – Input and Output Writing Output to the Monitor

// Demonstrate System.out.write(). Java program WriteDemo.java

public class WriteDemo

{


{

int b; // Program prints an ‘X’ on the monitor

b = 'X'; // The character is an int

System.out.write(b); // A byte stream; write low-order 8 bits

System.out.write('\n'); // Print a newline character \n

} // End of main( ) // print() and println() are easier to use than write()

} // End of class WriteDemo


Patrick Healy

Class #15 – Input and Output Stream classes (Bytes & Characters) The java.io package provides two categories of classes:

Byte stream readers and writers Character stream readers and writers

At the top of the hierarchy for stream classes are the abstract classes InputStream and Output Stream

The subclasses branch out and specializes into the different types of streams that they handle.

InputData, OutputData, and ObjectInput interfaces are implemented by the classes that handle data, such as, int, double, char, etc., and objects. Only ObjectInput specifies methods for reading objects.

DataInputStream - which is a subclass of FilterInputStream, which in turn is a subclass of InputStream – implements the InputData interface and can read primitive data, and objects from byte streams.


Patrick Healy

Class #15 – Input and Output Stream Classes FileInputStream can read raw streams of data from files. DataOutputStream can write primitive data; this class implements the

OutputData interface RandomAccessFile implements both InputData and OutputData

interfaces, therefore, it can read and write data to streams. ObjectOutputStream implements the ObjectOutput interface and can

write object data to streams.


Patrick Healy


InputStream Class (for reading bytes)

The following methods are defined in InputStream

and are often useful: public abstract int read() throws IOException

Reads the next byte and returns its value in the range of 0 to 255. At the end of the stream, it returns a - 1.

public int read(byte b[]) throws IOException

Reads bytes into array b,, returns b.length if the number of available bytes is >= b.length. Returns the number of bytes read if the number of available bytes is < than b.length, and returns –1 at the end of the stream.


Patrick Healy



The following methods are defined in InputStream and are often useful:

public void close() throws IOException

This method closes the input stream.

public void available() throws IOException

Returns the number of bytes that can be read from the input stream without blocking.


Patrick Healy



The following method is defined in InputStream and is often useful:

public long skip(long n) throws IOException

Skip over and discard n bytes of data from the input stream. The actual number of bytes skipped is returned.


Patrick Healy

Class #15 – Input and Output Reading & Writing Files Using Byte Streams To create a byte stream linked to a file, use FileInputStream or

FileOutputStream To open a file, create an object of one of these classes, specifying the

name of the file as an argument to the constructor. Once the file is open, you can read from the file or write to the file. To read form a file, you may use the read( ) method.

int read( ) throws IOException When you are done with a file, you should close it by calling close()

void close( ) throws IOException Closing a file releases the system resources allocated to the file,

allowing them to be used by another file.


Patrick Healy

Class #15 – Input and Output Reading & Writing Files Using Byte Streams

/* Display a text file.

To use this program, specify the name

of the file that you want to see.

For example, to see a file called TEST.TXT,

use the following command line.

Command line usage: java ShowFile TEST.TXT */

// Program ShowFile.java follows on the next slide ->


Patrick Healy

Class #15 – Input and Output Reading & Writing Files Using Byte Streamspublic class ShowFile { public static void main(String[ ] args) throws IOException { int i; FileInputStream fin; // Declare file pointertry { fin = new FileInputStream(args[0]); } // Open the input file catch(FileNotFoundException exc) { System.out.println(“Error: “ + exc.getMessage( )); System.out.println("File Not Found"); return; } } catch(ArrayIndexOutOfBoundsException exc) { System.out.println(“Error: “ + exc.getMessage( )); System.out.println("Usage is: java ShowFile File.txt "); return; }


Patrick Healy

Class #15 – Input and Output Reading & Writing Files Using Byte Streams

// Read bytes until EOF is encountered

do {

i = fin.read( ); // Read an integer

if(i != -1) System.out.print((char) i); // Cast the int as a char

} while( i != -1); // When i = -1, EOF is encountered

fin.close( ); // Close the input file

} // End of main method

} // End of class ShowFile


Patrick Healy

Class #15 – Input and Output Writing to a File Using Byte Streams

/* Java program to Copy a text file.

To use this program, specify the name

of the source file and the destination file.

For example, to copy a file called File1.txt

to a file called File2.txt , use the following

on the command line:

Usage: java CopyFile File1.txt File2.txt */


Patrick Healy


// CopyFile.java Demo byte stream file operations

import java.io.*;

public class CopyFile {

public static void main(String[ ] args) throws IOException

{

int i;

FileInputStream fin; // Declare 2 byte stream files (pointers)

FileOutputStream fout; // Output file pointer


Patrick Healy


try { // outer try block

// try to open input file

try { // inner try

fin = new FileInputStream(args[0]);

} catch(FileNotFoundException exc) {

System.out.println(“Error:”

+ exc.getMessage( ) );

System.out.println("Input File Not Found");

return; }


Patrick Healy


// open output file

try {

fout = new FileOutputStream(args[1]);

} catch(FileNotFoundException exc) {

System.out.println(“Error: “ + exc.getMessage());

System.out.println("Error Opening Output File");

return;

}

} // End of outer try block


Patrick Healy

Class #15 – Input and Output Writing to a File Using Byte Streams catch(ArrayIndexOutOfBoundsException exc) {

System.out.println(“Error: “ + exc.getMessage( ) );

System.out.println("Usage: CopyFile File1 File2");

return; }

try { // Try to copy file1 to file2

do {

i = fin.read( ); // Read a byte

if(i != -1) fout.write(i); // Write the byte to the output file

} while(i != -1); // Loop while not at EOF (-1)

} // End of try block

catch(IOException exc)

{ System.out.println("File Error"); }

fin.close( ); // Close the input file

fout.close( ); // Close the output file

} // End of main( ) method

} // End of class CopyFile


Patrick Healy

Class #15 – Input and Output Reading & Writing Binary Data So far, we have been reading and writing bytes containing ASCII bytes. You may want to create a file that contains other types of data such as

integers, doubles, or shorts , that is: int, double, short, etc. In Java, to read and write binary values of the simple Java data types,

you should use:

DataInputStream and DataOutputStream (for binary data)

DataOutputStream implements the OutputData interface. The OutputData interface defines methods that write all of Java’s

simple data types to a file.


Patrick Healy

Class #15 – Input and Output Reading & Writing Binary Data Note: Binary data is NOT in human-readable text format, obviously.

The constructor for DataOutputStream is:

DataOutputStream(OutputStream outputStream)

outputStream is the stream to which the binary data is written.


Patrick Healy

Class #15 – Input and Output Reading & Writing Binary Data The constructor for DataInputStream is:

DataInputStream(InputStream inputStream)

inputStream is the stream that is linked to the instance of

DataInputStream being created.

DataInputStream implements the DataInput interface which provides the methods for reading all of Java’s simple data types.

DataInputStream uses an InputStream instance as its foundation, overlaying it with methods that read the various Java data types.


Patrick Healy

Class #15 – Input and Output Reading & Writing Binary Data Examples

To create an input stream for the file in.dat ( bytes)

DataInputStream infile =

new DataInputStream(new FileInputStream(“in.dat”));

To create an output stream for the file out.dat:

DataOutputStream outfile =

new DataOutputStream(new FileOutputStream(“out.dat”));


Patrick Healy

Class #15 – Input and Output Reading & Writing Binary Data Common Input Methods Defined by DataInputStream (a byte stream)

Input Method Purpose

boolean readBoolean ( ) Reads a boolean

byte readByte ( ) Reads a byte

char readChar ( ) Reads a char

double readDouble( ) Reads a double

float readFloat ( ) Reads a float

int readInt ( ) Reads an int

long readLong ( ) Reads a long

short readShort ( ) Reads a short


Patrick Healy

Class #15 – Input and Output Reading & Writing Binary Data Common Output Methods Defined by DataOutputStream ( byte stream)

Output Method Purpose

void writeBoolean (boolean val) writes the boolean specified by val

void writeByte (int val) writes the low-order byte val

void writeChar(int val) writes the value val as a char

void writeDouble(double val) writes the double val

void writeFloat(float val) writes the float val

void writeInt(int val) writes the int val

void writeLong(long val) writes the long val

void writeShort(int val) writes val as a short


Patrick Healy

Class #15 – Input and Output Reading & Writing Binary Data Here is a Java program that demonstrates DataOutputStream and

DataInputStream. It writes and then reads back various types of data to and from a file.

// Write and then read back binary data.

import java.io.*;

public class RWData {


{

DataOutputStream dataOut; // Declare output, input file pointers

DataInputStream dataIn;


Patrick Healy

Class #15 – Input and Output Reading & Writing Binary Data

int i = 120;

double d = 1049.56;

boolean b = true;

try {

dataOut = new

DataOutputStream(new FileOutputStream(“testdata")); }

catch(IOException exc) {

System.out.println(“Error: “ + exc.getMessage( ));

System.out.println("Cannot open file.");

return; }


Patrick Healy

Class #15 – Input and Output Reading & Writing Binary Datatry { // Write the binary data

System.out.println("Writing " + i);

dataOut.writeInt(i);

System.out.println("Writing " + d);

dataOut.writeDouble(d);

System.out.println("Writing " + b);

dataOut.writeBoolean(b);

System.out.println("Writing " + 12.2 * 7.4);

dataOut.writeDouble(12.2 * 7.4);

}


Patrick Healy

Class #15 – Input and Output Reading & Writing Binary Data catch(IOException exc) {

System.out.println("Write error: + exc.getMessage( )");

}

dataOut.close( );

System.out.println(); // Print a blank line

// Now, read them back.

try {

dataIn = new

DataInputStream(new FileInputStream("testdata"));

}


System.out.println("Cannot open file. + exc.getMessage( )");

return;

}


Patrick Healy


try { // Read the binary data

i = dataIn.readInt();

System.out.println("Reading " + i);

d = dataIn.readDouble();

System.out.println("Reading " + d);

b = dataIn.readBoolean();

System.out.println("Reading " + b);

d = dataIn.readDouble();

System.out.println("Reading " + d);

}


Patrick Healy



System.out.println("Read error.“ + exc.getMessage( ) ); }

dataIn.close();

} // End of main ( )

} // End of class RWData

The output from the previous program follows:

Writing 120 Reading 120

Writing 1023.56 Reading 1049.56

Writing true Reading true

Writing 90.28 Reading 90.28


Patrick Healy


Reader class methods for reading characters

The Reader class is similar to the InputStream class. The methods in Reader are subject to character interpretation.

Remember: A character is 2 bytes ! public abstract int read() throws IOException

public int read(char b[]) throws IOException


public void skip() throws IOException


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Class #15 – Input and Output OutputStream ( bytes) & Writer (for characters)

Like InputStream (for reading bytes) and Reader (for reading characters), OutputStream and Writer are the counterparts.

They are the base classes for for all output streams of bytes and characters, respectively.

The next slide shows methods which are in both OutputStream and Writer.

See next slide ->


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OutputStream (Writing bytes)

public abstract void write(int b) throws IOException

Write a byte b (for OutputStream) or a charcter (for Writer)

public void write(byte[] b) throws IOException

This method writes all bytes in the array b to the output stream (for OutputStream) or characters in the array of characters (for Writer)


This method closes the output stream.

public void flush() throws IOException

Flush the output stream and send any buffered data in the stream to its destination.


Patrick Healy

Class #15 – Input and Output Writer (Writing characters) (Same as OutputStream)

public abstract void write(int b) throws IOException

Write a byte b (for OutputStream) or a character (for Writer)

public void write(byte[] b) throws IOException

This method writes all bytes in the array b to the output stream (for OutputStream) or characters in the array of characters (for Writer)


This method closes the output stream.

public void flush() throws IOException

Flush the output stream and send any buffered data in the stream to its destination.


Patrick Healy

Class #15 – Input and Output Console Input using Character Streams

For Java code that will be internationalized, inputting data from the console using Java’s character-based streams is a better, more convenient way to read characters from the keyboard than using byte streams.

Since System.in is a byte-stream, you need to wrap System.in inside of some type of Reader.

The best class for reading console input is BufferedReader which supports a buffered input stream. (BufferedReader inherits from Reader)

But, you cannot construct a BufferedReader directly from System.in


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You must first convert the input from System.in from a byte stream into a character stream. To do this, you must use InputStreamReader.

InputStreamReader converts bytes to characters.

To obtain an InputStreamReader object that is linked to System.in, use the following constructor:

InputStreamReader ( InputStream inputStream )

Since System.in refers to an object of type InputStream, it can be used for inputStream such as in: InputStreamReader(System.in)


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Next, using the object produced by InputStreamReader, construct a BufferedReader using the following constructor:

BufferedReader(Reader inputReader)

Here, inputReader is the stream that is linked to the instance of BufferedReader being created.


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Putting it all together, the following line of code creates a BufferReader that is connected to the keyboard.

BufferedReader br =

new BufferedReader( new InputStreamReader(System.in));

After the above statement executes, “br” will be a character-based

stream that is linked to the console thru System.in (which reads bytes)


Patrick Healy

Class #15 – Input and Output Console Input using Character Streams Reading Characters

Characters can be read from System.in using the read( ) method defined by BufferedReader.

BufferedReader defines the following versions of read( ) int read( ) throws IOException int read(char data[ ] ) throws IOException int read(char data[ ], int start, int max) throws IOException


Patrick Healy

Class #15 – Input and Output Console Input using Character Streams int read( ) throws IOException

reads a single Unicode character and returns a -1 when the end of the stream is reached.

int read(char data[ ]) throws IOException

reads characters from the input stream until:

(1) the array is full, (2) EOF is reached, or (3) an error occurs. int read(char data[ ], int start, int max) throws IOException

reads input into array data beginning at the location specified by start, storing up to max characters. It returns the number of characters read or -1 when the end of the stream is reached.

Pressing the [Enter] key generates an end-of-stream condition.


Patrick Healy

Class #15 – Input and Output Console Input using Character Streams The following program demonstrates the read( ) method by reading

characters from the console until the user types a period.

// Use a BufferedReader to read characters from the console.

import java.io.*;

public class ReadChars {


{


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BufferedReader br = new

BufferedReader(new InputStreamReader(System.in));

System.out.println("Enter some characters; period to quit.");

// read characters

do {

c = (char) br.read(); // Cast the character to a byte

System.out.println(c); // Print the character

} while(c != '.'); // Loop as long as the input char is not a period


} // End of ReadChars class


Patrick Healy

Class #15 – Input and Output Console Input using Character Streams Output from the previous program could be:

Enter some characters; period to quit.

I

T

P

J

A

V

A

. <- note the period character which stopped the input stream


Patrick Healy

Class #15 – Input and Output Console Input using Character Streams Reading Character Strings from the Keyboard …

To read a string from the keyboard, use the version of readLine( ) that is a member of the BufferedReader class. The general form is:

String readLine( ) throws IOException

It returns a string object that contains the characters read. It returns null if an attempt is made to read beyond the end of the stream.


Patrick Healy


The following program demonstrates BufferedReader and the readLine() method. The program reads and displays lines of text until the user enters the word “stop”

// Read a string from console using a BufferedReader.

import java.io.*;

class ReadLines {


throws IOException

{

// create a BufferedReader using System.in

BufferedReader br = new BufferedReader(new

InputStreamReader(System.in));

String str;


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System.out.println("Enter lines of text.");

System.out.println("Enter 'stop' to quit.");

do {

str = br.readLine();

System.out.println(str);

} while(!str.equals("stop"));


} // End of class ReadLines


Patrick Healy

Class #15 – Input and Output Console Output using Character Streams The preferred method of writing to the console (monitor) when using

Java is through a PrintWriter stream. PrintWriter is one of the character-based classes. Using a character-based class makes it easier to internationalize

Java programs. PrintWriter has several constructors, but this is the one to be used in

the demonstration program which is on the following slides:

PrintWriter(OutputStream outputStream, boolean flushOnNewline)


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Class #15 – Input and Output Console Output using Character Streams

PrintWriter(OutputStream outputStream, boolean flushOnNewline)

Here, outputStream is an object of type OutputStream.

flushOnNewLine controls whether Java flushes the output stream every time a println( ) method is called.

If flushOnNewLine is true flushing automatically takes place.

If flushOnNewLine is false, flushing is not automatic.


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To write to the console (monitor) using a PrintWriter, specify System.out for the output stream and flush the stream after each call to println( ).

For example, the following line of code creates a PrintWriter that is connected to console (monitor) output.

PrintWriter pw = new PrintWriter(System.out, true);

The Java program on the next slide demonstrates a PrintWriter


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// Demonstrate PrintWriter.

import java.io.*;

public class PrintWriterDemo {

public static void main(String[ ] args) {

PrintWriter pw = new PrintWriter(System.out, true);

int i = 120;

double d = 123.67;


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pw.println("Using a PrintWriter."); // PrintWriter Demo

pw.println(i);

pw.println(d);

pw.println(i + " + " + d + " is " + i +d);


} // End of class PrintWriterDemo

The output from the previous program is:

Using a PrintWriter.

120

123.67

120 + 123.67 is 243.67


Patrick Healy

Class #15 – Input and Output File Input & Output using Character Streams

In general, to perform character-based file I/O, you will use the FileReader and FileWriter classes.

Using a FileWriter

FileWriter creates a Writer that you can use to write to a file.

FileWriter is derived from OutputStreamWriter and Writer classes

Commonly used constructors are:

FileWriter (String fileName) throws IOException

FileWriter (String fileName, boolean append) throws IOException

fileName is the full path name of the file. If append is true, then output is appended to the end of the file. Otherwise, the file is overwritten.


Patrick Healy

Class #15 – Input and Output File I / O using Character Streams FileWriter

// A simple keyboard-to-disk utility that demonstrates a FileWriter.

import java.io.*;

public class KtoD {



String str;

FileWriter fw;

BufferedReader br =

new BufferedReader( new InputStreamReader(System.in));


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try {

fw = new FileWriter("test.txt"); // Try to open the file

}



System.out.println("Cannot open output file.");

return ;

}


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System.out.println("Enter text ('stop' to quit).");

do {

System.out.print(": ");

str = br.readLine( );

if(str.compareTo("stop") == 0) break;

str = str + "\r\n"; // add carriage return & newline

fw.write(str);

} while(str.compareTo("stop") != 0);

fw.close( );

} // End of main ( ) method

} // End of class KtoD


Patrick Healy

Class #15 – Input and Output File I / O using Character Streams FileReader

The FileReader class creates a Reader that you can use to read the

contents of a file. FileReader is derived from the InputStreamReader and Reader classes. It has access to the methods in those classes.

The most common constructor is:

FileReader(String fileName) throws FileNotFoundException

where fileName is the full path name of the file.

It throws a FileNotFoundException if the file does not exist.


Patrick Healy


The following program reads a text file called “test.txt” and displays the information on the screen.

// A simple disk-to-screen utilitiy that demonstrates a FileReader.

import java.io.*;

class DtoS {

public static void main(String[ ] args) throws Exception

{

FileReader fr = new FileReader("test.txt");

BufferedReader br = new BufferedReader(fr);

String s;


Patrick Healy


while((s = br.readLine()) != null)

{

System.out.println(s);

}

fr.close( ); // Close the file


} // End of DtoS class


Patrick Healy


The File Class: Objectives To discover file properties, delete and rename files using the File class To understand how I/O is processed in Java To distinguish between text I/O and binary I/O To read and write characters using FileReader and FileWriter To improve the performance of text I/O using BufferedReader and BufferedWriter To write primitive values, strings, and objects as text using PrintWriter and PrintStream To read and write bytes using FileInputStream and FileOutputStream To read and write primitive values and strings using

DataInputStream/DataOutputStream To store and restore objects using ObjectOutputStream and ObjectInputStream, and to

understand how objects are serialized and what kind of objects can be serialized To use RandomAccessFile for both read and write.


Patrick Healy


The File Class

The File class is intended to provide an abstraction that deals with most of the machine-dependent complexities of files and path names in a machine-independent fashion. The filename is a string.

The File class is a wrapper class for the file name and its directory path.


Patrick Healy

Class #15 – Input and Output java.io.File

+File(pathname: String)

+File(parent: String, child: String)

+File(parent: File, child: String)

+exists(): boolean

+canRead(): boolean

+canWrite(): boolean

+isDirectory(): boolean

+isFile(): boolean

+isAbsolute(): boolean

+isHidden(): boolean

+getAbsolutePath(): String

+getCanonicalPath(): String

+getName(): String

+getPath(): String

+getParent(): String

+lastModified(): long

+delete(): boolean

+renameTo(dest: File): Boolean

Creates a File object for the specified pathname. The pathname may be a directory or a file.

Creates a File object for the child under the directory parent. child may be a filename or a subdirectory.

Creates a File object for the child under the directory parent. parent is a File object. In the preceding constructor, the parent is a string.

Returns true if the file or the directory represented by the File object exists.

Returns true if the file represented by the File object exists and can be read.

Returns true if the file represented by the File object exists and can be written.

Returns true if the File object represents a directory.

Returns true if the File object represents a file.

Returns true if the File object is created using an absolute path name.

Returns true if the file represented in the File object is hidden. The exact definition of hidden is system-dependent. On Windows, you can mark a file hidden in the File Properties dialog box. On Unix systems, a file is hidden if its name begins with a period character '.'.

Returns the complete absolute file or directory name represented by the File object.

Returns the same as getAbsolutePath() except that it removes redundant names, such as "." and "..", from the pathname, resolves symbolic links (on Unix platforms), and converts drive letters to standard uppercase (on Win32 platforms).

Returns the last name of the complete directory and file name represented by the File object. For example, new File("c:\\book\\test.dat").getName() returns test.dat.

Returns the complete directory and file name represented by the File object. For example, new File("c:\\book\\test.dat").getPath() returns c:\book\test.dat.

Returns the complete parent directory of the current directory or the file represented by the File object. For example, new File("c:\\book\\test.dat").getParent() returns c:\book.

Returns the time that the file was last modified.

Deletes this file. The method returns true if the deletion succeeds.

Renames this file. The method returns true if the operation succeeds.

Obtaining file properties and manipulating file


Patrick Healy

Class #15 – Input and Output Example Using the File Class TestFileClass.java

Objective: Write a program that demonstrates how to create files in a platform-independent way and use the methods in the File class to obtain their properties. Figure 1 shows a sample run of the program on Windows, and Figure 2 a sample run on Unix (Windows) (Unix)


Patrick Healy

Class #15 – Input and Output The File Class and Processing External Files The File class provides an abstraction that deals with most of the

machine-dependent complexities of files and path names in a machine-independent fashion.

You can create a new File object using the following statement:

File myfile = new File (“myfile.dat”);

You can use the File class to check properties of files, such as whether the file exists, or is readable, or updateable.


Patrick Healy

Class #15 – Input and Output The File Class and Processing External Files You can use the getName( ) method to get the name of the file. For example,

if (myfile.exists( ) )

System.out.println(“File “ + myfile.getName( ) + “ already exists”);

The following statement creates a file using the full path using the Windows operating system:

File myfile = new File(“C:\\Java\\myfile.data”);


Patrick Healy

Class #15 – Input and Output The File Class and Processing External Files You can use the getPath( ) method to get the full path of the file and

the getParent( ) method to get the directory that contains the file. For example,

if (myfile.exists( ) )

{

System.out.println(“The full path is “ + myfile.getPath( ) );

System.out.println(“The directory is “ + myfile.getParent( ) );

}


Patrick Healy

Class #15 – Input and Output Demo Program: TestFileClass.java// TestFileClass.java: Demonstrate the File class Chapt 18 I/O ITP120import java.io.*;import java.util.*;

public class TestFileClass { public static void main(String[] args) { // Create a File object File file = new File(".", "images" + File.separator + "bill_gates.gif"); System.out.println("Does it exist? " + file.exists()); System.out.println("Can it be read? " + file.canRead()); System.out.println("Can it be written? " + file.canRead()); System.out.println("Is it a directory? " + file.isDirectory()); System.out.println("Is it a file? " + file.isFile()); System.out.println("Is it absolute? " + file.isAbsolute()); System.out.println("Is it hidden? " + file.isHidden()); System.out.println("What is its absolute path? " + file.getAbsolutePath());


Patrick Healy

Class #15 – Input and Output Demo Program: TestFileClass.java try { System.out.println("What is its canonical path? " + file.getCanonicalPath()); } catch (IOException ex) { }

System.out.println("What is its name? " + file.getName()); System.out.println("What is its path? " + file.getPath()); System.out.println("When was it last modified? " + new Date(file.lastModified()));

System.out.println("What is the path separator? " + File.pathSeparatorChar); System.out.println("What is the name separator? " + File.separatorChar); }}


Patrick Healy


Processing External Files

Again, you must use file streams to read from or writeto a disk file.

Once again, you can use FileInputStream or FileOutputStream for byte streams.

And you can use FileReader or FileWriter for character streams.


Patrick Healy

Class #15 – Input and Output File I/O Stream Constructors

To create a file stream, use these constructors:

public FileInputStream (String filenameString) // Byte stream constructors

public FileInputStream (File file)

public FileOutputStream (String filenameString) // Byte stream constructor

public FileOutputStream (File file)

public FileReader (String filenameString) // Character stream constructors

public FileReader (File file)

public FileWriter (String filenameString) // Character stream constructor

public FileWriter (File file)


Patrick Healy


File I/O Stream Constructors

Constructing instances of FileInputStream, FileOutputStream, FileReader, and FileWriter from file names:

FileInputStream infile = new FileInputStream("in.dat");

FileOutputStream outfile = new FileOutputStream("out.dat");

FileReader infile = new FileReader("in.dat");

FileWriter outfile = new FileWriter("out.dat");


Patrick Healy

Class #15 – Input and Output Demo Program: TestFileReader.java// TestFileReader.java Chapter 18 I/O ITP 120import java.io.*;public class TestFileReader { public static void main(String[ ] args) { FileReader input = null; try { // Create an input stream input = new FileReader("temp.txt"); int code; // Repeatedly read a character and display it on the console while ((code = input.read()) != -1) System.out.print((char)code); } // End of try block


Patrick Healy

Class #15 – Input and Output Demo Program: TestFileReader.javaSystem.out.println("File temp.txt does not exist"); } catch (IOException ex) { ex.printStackTrace(); } finally { try { input.close(); // Close the stream } catch (IOException ex) { ex.printStackTrace(); } } } // End of class TestFileReader


Patrick Healy

Class #15 – Input and Output Demo Program: TestFileWriter.java// TestFileWriter.java Chapter 18 File I/O ITP 120import java.io.*;

public class TestFileWriter { public static void main(String[ ] args) throws IOException { // Create an output stream to the file FileWriter output = new FileWriter("temp.txt", true);

// Output a string to the file output.write(“ NVCC Introduction to Java Programming ITP 120 !!!");

// Close the stream output.close(); }}


Patrick Healy

Class #15 – Input and Output Processing External Files


Patrick Healy

Class #15 – Input and Output Processing External Files The previous diagram shows that:

FileInputStream, fis, is used to read data (bytes) from a file

FileOutputStream, fos, is used to write data (bytes) to a file

Command line:

java CopyFileUsingByteStream f1.txt f2.txt

See the Java program CopyFileUsingByteStream on the following slides


Patrick Healy


// CopyFileUsingByteStream.java For Copying files (byte streams)

import java.io.*;

public class CopyFileUsingByteStream

{

// Main method: args[0] for sourcefile and args[1] for target file


{

// Declare input and output file streams

FileInputStream fis = null;

FileOutputStream fos = null;


Patrick Healy


if (args.length !=2) // args[0] is source file

{ // args[1] is target file

System.out.println(

"Usage: java CopyFileUsingByteStream f1 f2");

System.exit(0); // Stop the program

}


Patrick Healy


try

{

// Create file input stream

fis = new FileInputStream(new File(args[0]));

// Create file output stream if the file does not exist

File outFile = new File(args[1]);

if (outFile.exists())

{

System.out.println("file " + args[1] + " already exists");

return;

}


Patrick Healy


else

fos = new FileOutputStream(args[1]); // FileOutputStream

// Display the file size

System.out.println("The file " + args[0] + " has "+

fis.available() + " bytes");


Patrick Healy


// Continuously read a byte from fis and write it to fos

int r;

while ((r = fis.read()) != -1) // EOF is -1

fos.write((byte)r);

}

catch (FileNotFoundException ex)

{

System.out.println(“Error: “ + ex.getMessage( ) );

System.out.println("File not found: " + args[0]);

}


Patrick Healy


catch (IOException ex)

{

System.out.println(“Some IO Exception occurred”);

System.out.println(“Error: “ + ex.getMessage( ));

}

Continues to next slide


Patrick Healy

Class #15 – Input and Output Processing External Files finally

{

try

{

if (fis != null) fis.close(); // Close the input & output files

if (fos != null) fos.close();

}


{


}

} // End of finally block


} // End of class CopyFileUsingByteStream


Patrick Healy

Class #15 – Input and Output Filter Streams

Filter streams are streams that filter bytes or characters for some purpose.

If you want to read integers, doubles, or Strings, you need a filter class to wrap the input stream.

Using a filter class enables you to read integers, doubles, and strings instead of bytes and characters.

Use FilterInputStream and FilterOutputStream when you need to process primitive numeric types.


Patrick Healy

Class #15 – Input and Output Filter Streams To process strings, use BufferedReader and PushbackReader to filter

characters.

Note: FilterInputStream and FilterOutputStream are abstract classes.


Patrick Healy

Class #15 – Input and Output FilterInputStream subclasses DataInputStream handles binary formats for all primitive data types.

BufferedInputStream gets data from the buffer and then reads them from the stream if necessary.

LineNumberInputStream keeps track of how many lines are read.

PushBackInputStream allows single-byte look-a-head. Looks at a byte and pushes it back to the stream if the byte read is NOT the desired byte.


Patrick Healy

Class #15 – Input and Output FilterOutputStream subclasses

DataOutputStream outputs the binary formats for all primitive data types which is useful if another program uses the output.

BufferedOutputStream outputs to the buffer first and then to the stream if necessary. You may also call the flush( ) method to write the buffer to the stream.

PrintStream outputs the Unicode format of all primitive types which is useful if the format is output to the console.


Patrick Healy


Data Streams (bytes)

The data streams (DataInputStream and DataOutputStream)

read and write Java primitive types in a machine-independent

fashion.

This enables you to write a data file for one computer

and read it on another computer that has a different operating system or file structure.


Patrick Healy

Class #15 – Input and Output DataInputStream Methods defined in the DataInput Interface

int readByte() throws IOException

int readShort() throws IOException

int readInt() throws IOException

int readLong() throws IOException

float readFloat() throws IOException

double readDouble() throws IOException

char readChar() throws IOException

boolean readBoolean() throws IOException

String readUTF() throws IOException


Patrick Healy

Class #15 – Input and Output DataOutputStream Methods defined in the DataOutput interface

void writeByte(byte b) throws IOException

void writeShort(short is) throws IOException

void writeInt(int i) throws IOException

void writeLong(long l) throws IOException

void writeFloat(float f) throws IOException

void writeDouble(double d) throws IOException

void writeChar(char c) throws IOException

void writeBoolean(boolean b) throws IOException

void writeBytes(String s) throws IOException

void writeChars(String s) throws IOException

void writeUTF(String s) throws IOException


Patrick Healy


DataInputStream & DataOutput Stream Constructors

Data streams are used as wrappers on existing input and output streams to filter data in the original stream.

DataInputStream infile = newDataInputStream(new FileInputStream("in.dat"));

The above creates an input file for in.dat.

DataOutputStream outfile = newDataOutputStream(new FileOutputStream("out.dat"));

The above creates an output file for out.dat.


Patrick Healy

Class #15 – Input and Output Using Data Streams

The next example shows a program that:

1) Creates 10 random integers,

2) Stores them in a data file,

3) Retrieves data from the file,

4) Displays the integers on the console.

See next slide


Patrick Healy

Class #15 – Input and Output Using Data Streams Demo Example

// TestDataStreams.java: Create a file, store it in binary form, and

// display the contents of the file on the console

import java.io.*;

public class TestDataStreams

{

// Main method


{

// Declare data input and output streams

DataInputStream dis = null;

DataOutputStream dos = null;


Patrick Healy


// Construct a temp file

File tempFile = new File("mytemp.dat");

// Check if the temp file exists

if (tempFile.exists())

{

System.out.println("The file mytemp.dat already exists,"

+" delete it, rerun the program");

System.exit(0);

}


Patrick Healy


// Write data

try

{

// Create data output stream for tempFile

dos = new DataOutputStream(new

FileOutputStream(tempFile));

for (int i=0; i<10; i++)

dos.writeInt((int)(Math.random()*1000));

}


Patrick Healy



{

System.out.println(ex.getMessage( ) );

}

finally

{

try

{

if (dos != null) dos.close( ); // Close the file(s)

}


{ System.out.println(“Error: “ + ex.getMessage( ) ); }


Patrick Healy


// Read data

try

{

// Create data input stream

dis = new DataInputStream(new FileInputStream(tempFile));

for (int i=0; i<10; i++)

System.out.print(" "+dis.readInt ( ) ); // Display the integers

}


Patrick Healy



{

System.out.println("File not found“ + ex.getMessage( ) ););

}


{

System.out.println(ex.getMessage());

}


Patrick Healy


finally

{

try

{

if (dis != null) dis.close( ); // Close the file(s)

}


{

System.out.println(“Error: “ + ex.getMessage( ) ));

}



} // End of class TestDataStreams


Patrick Healy

Class #15 – Input and Output Using Data Streams Demo Example The previous Java program TestDataStreams.java creates a

DataInputStream object named “dis” wrapped on FileInputStream and creates a DataOutputStream object “dos” wrapped on FileOutputStream

Conceptually,

Program DataInputStream dis <-- fileInputStream <--mytemp.dat

DataOutputStream dos fileOutputStream mytemp.dat

The program uses a temporary file, mytemp.dat, to store data.

The program creates mytemp.dat if it does not exist and writes 10 random

integers into mytemp.dat. The data in mytemp.dat is in binary format.


Patrick Healy

Class #15 – Input and Output Character Classes The classes that handle characters have at the top of their hierarchy,

Reader and Writer The subclasses branch out to provide specialized functionality.

FileReader provides functionality for reading streams of characters from files.

BufferedReader buffers character streams for efficiency

FileWriter for writing character streams to files.

PrintWriter for writing character streams.


Patrick Healy

Class #15 – Input and Output File Class

File class provides functionality for working directly with files in the operating system

The File class provides overloaded constructors for creating File objects. A File object can be created by giving the name of the file:

File inputFile = new File(“in.dat”); // Same directory File myInputFile = new File(“C:\\myDirectory\\in.dat”);

A File Object can refer to either a file or directory File theDir = new File(“C:\\myDir”); //File object theDir refers to a directory

Some File class methods: exists() that tests if the named file already exist. mkdir( String st ) for creating directories list() for listing the contents of directories getPath() gets the path of the named file length() returns the file size in bytes


Patrick Healy

Class #15 – Input and Output File Class

Example: DirectoryContents.java listing the contents of a directory using File class

import java.io.*;

public class DirectoryContents

{


{

File myDir = new File(“C:\\");

if(myDir.isDirectory( ) ) {

System.out.println("Contents of directory " + myDir );

String[ ] contents = myDir.list();

for( int I = 0; I < contents.length; I++)

System.out.println(contents[ I ] );

} // End of “if” block


} // End of class DirectoryContents


Patrick Healy

Class #15 – Input and Output Using Java I/O

Many of the methods including constructors of Java.io classes throw exceptions:

The most commonly thrown is IOException. Reading data from the keyboard

BufferedReader in = new BufferedReader(new InputStreamReader(System.in); An InputStreamReader is like an adapter, it reads byte streams

and converts it into character streams BufferedReader wraps the InputStreamReader to provide extra

functionality, allowing to buffer the input to support readLine()


Patrick Healy


Example Reading strings from the keyboard

Import java.io.*

public class ReadStringFromKeyboard {


{ // Converts from bytes to characters

BufferedReader in = new BufferedReader(new InputStreamReader (System.in));

String yourInput;

try {

System.out.println("Please enter any string and hit the return key when done:");

yourInput = in.readLine( );

System.out.println("\nBelow is the input you entered");

System.out.println(yourInput);

}

catch (IOException ex) { System.out.println(“Could not read from the keyboard” }


} // End of class ReadStringFromKeyboard


Patrick Healy


Example: Reading from an external filepublic class ReadFromFile {


{

String st = null;

File inputFileName = null;

FileReader inputFile = null;

BufferedReader in = null;

try {

inputFileName = new File("Input1.txt");

inputFile = new FileReader(inputFileName);

in = new BufferedReader(inputFile);

/* Note: The above 3 lines can be combined in one line as below

in = new BufferedReader(new FileReader(new File("Input1.txt"))); */


Patrick Healy


Example Continued // Now let us start reading from the opened file

while((st = br.readLine()) != null )

{

System.out.println(st); // Print the string

}

}

catch (FileNotFoundException fnex)

{ System.out.println(“Error: “ + fnex.getMessage( ) );

System.out.println("Input file was not found");

}

catch (IOException ex) { System.out.println(“Error: “ + ex.getMessage( ) );

System.out.println("There was a problem reading from the file");

}


Patrick Healy

Class #15 – Input and Output Using Java I/O Example continuedfinally

{

if( br != null)

try {

br.close( ); // Close the file

}

catch (Exception ex) {


System.out.println("There was a problem with closing the file");

}

} // End finally block


} // End of class


Patrick Healy


Print Streams

The data output stream outputs a binary representation of data, so you cannot view its contents as text.

In Java, you can use print streams to output data into files. These files can then be viewed as text.

The PrintStream and PrintWriter classes provide the functionality for doing this.

PrintStream is for bytes

PrintWriter is for characters (Unicode)


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Print Streams: PrintWriter Constructors

PrintWriter(Writer out)

PrintWriter(Writer out, boolean autoFlush)

PrintWriter(OutputStream out)

PrintWriter(OutputStream out, boolean autoFlush)


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Print Streams: PrintWriter Methods (for chars)

void print(Object o) void print(String s) void println(String s) void print(char c) void print(char[] cArray) void print(int i) void print(long l) void print(float f) void print(double d) void print(boolean b)


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Class #15 – Input and Output Print Streams: PrintWriter Methods Note:

On the previous slide, you may replace print with println in the various method definitions.

The println method, which prints the object, is followed by a new line.

When the object is passed to print or println,

the object’s toString( ) method converts it to a String object.


Patrick Healy

Class #15 – Input and Output Demo Program Example Using Print Streams The next sample Java program creates a print stream, pw, of

PrintWriter, wrapped on FileOutputStream, for text format.

pw = new PrintWriter(new FileOutputStream(tempFile),true);

The program creates the file, arg[0], if that file does not already exist. The program writes 10 random integers into the file by using the data

output stream, then closes the stream. The data file could be viewed by using the type command in DOS


Patrick Healy

Class #15 – Input and Output Using Print Streams: Demo Example

// TestPrintWriters.java: Create a text file

// using PrintWriter

import java.io.*;

public class TestPrintWriters

{

// Main method: args[0] is the output file

public static void main(String[] args)

{

// Declare print stream

PrintWriter pw = null;


Patrick Healy

Class #15 – Input and Output Using Print Streams: Demo example

// Check usage

if (args.length != 1)

{

System.out.println("Usage: java

TestPrintWriters file");

System.exit(0);

}

File tempFile = new File(args[0]);


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if (tempFile.exists())

{

System.out.println("The file " + args[0] +

" already exists, delete it, rerun the program");

System.exit(0);

}


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// Write data

try

{

// Create print writer stream for tempFile

pw = new PrintWriter(new FileOutputStream(tempFile), true);

for (int i=0; i<10; i++)

pw.print(" "+(int)(Math.random()*1000));

}


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{


}

finally

{

// Close files

if (pw != null) pw.close();

}

}

}


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C:\test>java TestPrintWriters

Usage: java TestPrintWriters filename

C:\test>java TestPrintWriters test.dat

C:\test>type test.dat (Use the TYPE command to see data in file)

567 915 7 23 677 455 402 997 290 549


Patrick Healy


Print Streams


Patrick Healy


Example: WriteToFile.java Writing text to external files

import java.io.File;

import java.io.FileWriter;

import java.io.PrintWriter;

import java.io.IOException;

public class WriteToFile {

public WriteToFile( )

{ } // Empty constructor


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Example: WriteToFile.java (continued)

public static void main (String[ ] args)

{

File outputFileName = null;

PrintWriter outToFile = null;

try {

outputFileName = new File("outFile1.txt");

outToFile = new PrintWriter( new FileWriter(outputFileName));

// Now we can start writing to file

outToFile.println("This message is going to the output file");

outToFile.println("This will be line two in the output file");

outToFile.println("We can write the output file any time we want");

outToFile.flush( ); // Flush output file

}


Patrick Healy

Class #15 – Input and Output Using Java I/O Example 18.6

catch (IOException ex) {


System.out.println("There was a problem writing to the output file");

}

finally {

if ( outToFile != null )

outToFile.close( ); // Close output file



} // End of class WriteToFile


Patrick Healy


Buffered Streams in Java

Java introduces buffered streams that speed up input and output by reducing the number of reads and writes. In the case of input, a bunch of data is read all at once instead of one byte at a time.

In the case of output, data are first cached into a buffer, then written all together to the file.

Using buffered streams is highly recommended.


Patrick Healy


Buffered Stream Constructors

BufferedInputStream (InputStream in)

BufferedInputStream (InputStream in, int bufferSize)

BufferedOutputStream (OutputStream in)

BufferedOutputStream (OutputStream in, int bufferSize)

BufferedReader(Reader in)

BufferedReader(Reader in, int bufferSize)

BufferedWriter(Writer out)

BufferedWriter(Writer out, int bufferSize)


Patrick Healy

Class #15 – Input and Output Demo Program: ViewFile.java (A Text Viewer program)

This case study writes a program that views a text file in a text area. The user enters a filename in a text field and clicks the View button; the file is then displayed in a text area.


Patrick Healy

Class #15 – Input and Output Buffered Streams in Java ViewFile program

// ViewFile.java: Read a text file and store it in a text area

import java.awt.*; // Buffered I/O example (Demo program)

import java.awt.event.*;

import java.io.*;

import javax.swing.*;

public class ViewFile extends MyFrameWithExitHandling

implements ActionListener

{

// Button to view view

private JButton jbtView = new JButton("View");


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// Text field to receive file name

private JTextField jtf = new JTextField(12);

// Text area to display file

private JTextArea jta = new JTextArea();

public static void main(String [ ] args) // Main method

{

ViewFile frame = new ViewFile();

frame.setTitle("View File Program in Java");

frame.setSize(400, 300);

frame.setVisible(true);

}


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// Constructor

public ViewFile()

{

// Panel p to hold a label, a text field, and a button

Panel p = new Panel();

p.setLayout(new BorderLayout());

p.add(new Label("Filename"), BorderLayout.WEST);

p.add(jtf, BorderLayout.CENTER);

jtf.setBackground(Color.yellow);

jtf.setForeground(Color.red);

p.add(jbtView, BorderLayout.EAST);


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// Add jtaFile to a scroll pane

JScrollPane jsp = new JScrollPane(jtaFile);

// Add jsp and p to the frame

getContentPane().add(jsp, BorderLayout.CENTER);

getContentPane().add(p, BorderLayout.SOUTH);

// Register listener

jbtView.addActionListener(this);

}


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// Handle the "View" button

public void actionPerformed(ActionEvent e)

{

if (e.getSource() == jbtView)

showFile();

}


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// Display the file in the text area

private void showFile()

{

// Use a BufferedStream to read text from the file

BufferedReader infile = null;

// Get file name from the input text field at the bottom

String filename = jtf.getText().trim();

String inLine;


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try

{

// Create a buffered stream

infile = new BufferedReader(new FileReader(filename));

// Read a line

inLine = infile.readLine();

boolean firstLine = true;


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while (inLine != null) // Append the line to the text area

{

if (firstLine) {

firstLine = false;

jtaFile.append(inLine); }

else

{

jta.append("\n" + inLine); }

inLine = infile.readLine();

}



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{ System.out.println(“Error: “ + ex.getMessage( ) );

System.out.println("File not found: " + filename);

}


{


}


Patrick Healy


finally

{

try

{

if (infile != null) infile.close( ); // Close input file

}


{


}


} // End of method showFile()

} // End of class ViewFile


Patrick Healy


Demostrate the ViewFile program by running:

java ViewFile (at the command prompt)

Wait for Java window to appear.

then type Comcast1.txt or the name of some text file in the text box at the bottom of the Java window.

Look at the contents on the text file in the Java window.


Patrick Healy

Class #15 – Input and Output Text Input & Output on the Console

In previous chapters, you used text input and output with the System class. The System class, as you have already seen, contains 3 I/O objects: System.in, System.out, and System.err. The objects in, out and err are static variables.

The variable in is of InputStream type and out , err are of PrintStream type. (byte streams)

These are the basic objects that all java programmers use to get input from the keyboard, send output to the screen, and display error messages.


Patrick Healy


To perform console output, you can use any of the methods for PrintStream in the System.out object.

To get input from the keyboard, you can use the following statements to read a string from the keyboard

See next slide

AND ALSO VIEW THE EXPANDED VERSION of MyInput.java which

follows thereafter


Patrick Healy


BufferedReader br

= new BufferedReader(new InputStreamReader(System.in), 1);

// Note: the 1 above means a buffer size of 1

// Declare and initialize the string

String string = " ";

// Get the string from the keyboard

try

{ string = br.readLine(); }


System.out.println(ex); }


Patrick Healy

Class #15 – Input and Output Text I/O on the Console MyInput.java (full)

public class MyInput // Expanded version

{ // Read a string from the keyboard

public static String readString()

{

BufferedReader br

= new BufferedReader(new InputStreamReader(System.in), 1);

// Declare and initialize the string

String string = " ";

// Get the string from the keyboard

try {

string = br.readLine(); }


System.out.println(ex) ; }


Patrick Healy


// Return the string obtained from the keyboard

return string;

}

// Read an int value from the keyboard

public static int readInt()

{

return Integer.parseInt(readString());

}


Patrick Healy


// Read a double value from the keyboard

public static double readDouble()

{

return Double.parseDouble(readString());

}

// Read a byte value from the keyboard

public static double readByte()

{

return Byte.parseByte(readString());

}


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// Read a short value from the keyboard

public static double readShort()

{

return Short.parseShort(readString());

}

// Read a long value from the keyboard

public static double readLong()

{

return Long.parseLong(readString());

}


Patrick Healy


// Read a float value from the keyboard

public static double readFloat()

{

return Float.parseFloat(readString());

}

}


Patrick Healy

Class #15 – Input and Output Random Access Files (byte streams) Java allows you to access the contents of a file in random order To do this, you will use RandomAccessFile which encapsulates a

random-access file. RandomAccessFile is a stream class derived from Object RandomAccessFile is NOT derived from InputStream or OutputStream. RandomAccessFile implements interfaces InputData & OutputData InputData & OutputData define the basic I/O methods. You can also position the file pointer within the file using the method

seek ( )


Patrick Healy

Class #15 – Input and Output Random Access Files (Constructor(s)) The constructor for RandomAccessFile is:

RandomAccessFile (String filename, String access)

throws FileNotFoundException

The name of the file is passed in filename

The term access determines what type of file access is permitted.

If the access is “r”, the file is read-only.

If the access is “rw”, the file is opened in read-write mode.


Patrick Healy

Class #15 – Input and Output Random Access Files (Methods) The method seek ( ) is used to set the current position of the file

pointer within a random access file:

void seek (long newpos) throws IOException

newpos specifies the new position, in bytes, of the file pointer from

the beginning of the file.

After a call to seek( ), the next read or write operation will occur at the

new file position.


Patrick Healy

Class #15 – Input and Output Random Access Files (Methods) public long getFilePointer ( ) throws IOException


public long length ( ) throws IOException

Returns the length of the file in bytes.

public final void writeChar (int v) throws IOException

Writes a character to the file as a 2-byte Unicode character with the higher byte written first.

public final void writeChars(String s) throws IOException

Writes a string to a file as a sequence of characters.


Patrick Healy

Class #15 – Input and Output Random Access Files RandomAccessFile implements the read ( ) and write ( ) methods.

It also implements the InputData and OutputData interfaces, which means that methods to read and write the simple data types such as readInt( ) and writeDouble( ) are available.

The slides which follow show a Java program that demonstrates random

access file I/O. The program writes 6 double numbers to a file and

then reads them back in a non-sequential order.


Patrick Healy

Class #15 – Input and Output Random Access Files

// Demonstrate random access files RandonAccessDemo.java

import java.io.*;

public class RandomAccessDemo {



double data[ ] = { 19.4, 10.1, 123.54, 33.0, 87.9, 74.25 };

double d;

RandomAccessFile raf;


Patrick Healy


try {

raf = new RandomAccessFile("random.dat", "rw");

}

catch(FileNotFoundException ex)

{

System.out.println("Cannot open file.");


return ;

}


Patrick Healy


// Write values to the file.

for (int i=0; i < data.length; i++) {

try {

raf.writeDouble(data[i]);

}

catch(IOException ex) {


System.out.println("Error writing to file.");

return ; }

} // End of “for” loop


Patrick Healy


try {

// Now, read back specific values

raf.seek(0); // seek to first double

d = raf.readDouble();

System.out.println("First value is " + d);

raf.seek(8); // seek to second double


System.out.println("Second value is " + d);

raf.seek(8 * 3); // seek to fourth double


System.out.println("Fourth value is " + d);

System.out.println();


Patrick Healy


// Now, read every other value.

System.out.println("Here is every other value: ");

for (int i=0; i < data.length; i+=2) {

raf.seek(8 * i); // seek to ith double


System.out.print(d + " ");

} // End of “for” loop



Patrick Healy


catch(IOException exc)

{


System.out.println("Error seeking or reading.");

}

raf.close( ); // Close the file

} // End of main ( )

} // End of class RandomAccessDemo


Patrick Healy

Class #15 – Input and Output Random Access Files Output from the previous Java program RandomAccessDemo:

First value is 19.4

Second value is 10.1

Fourth value is 33.0

Here is every other value:

19.4 123.54 87.9


Patrick Healy

Class #15 – Input and Output Case Studies: Address Book

Now let us use RandomAccessFile to create a useful project for storing and viewing and address book. The user interface of the program is shown in Figure 16.24. The Add button stores a new address to the end of the file. The First, Next, Previous, and Last buttons retrieve the first, next, previous, and last addresses from the file, respectively.


Patrick Healy


Parsing Text Files

The StreamTokenizer class lets you take an input stream and parse it into words, which are known as tokens.

The tokens are read one at a time.

The following is the StreamTokenizer constructor:

StreamTokenizer st = StreamTokenizer(Reader is)


Patrick Healy


StreamTokenizer Constants

TT_WORD

The token is a word.

TT_NUMBER

The token is a number.

TT_EOL

The end of the line has been read.

TT_EOF

The end of the file has been read.


Patrick Healy


StreamTokenizer Variables

int ttype (token type)

Contains the current token type, which matches one of the constants listed on the preceding slide.

double nval

Contains the value of the current token if that token is a number.

String sval

Contains a string that gives thecharacters of the current token if thattoken is a word.


Patrick Healy


StreamTokenizer Methods

public int nextToken() throws IOException

Parses the next token from the input stream of this StreamTokenizer.

The type of the next token is returned in the ttypefield.

If ttype == TT_WORD, the token is stored in sval;

if ttype == TT_NUMBER, the token is stored in nval.


Patrick Healy


Example : Demo program Using StreamTokenizer Demo: ParsingTextFile.java


Patrick Healy

Class #15 – Input and Output ParsingTextFile.java (Demo program)// ParsingTextFile.java: ITP 120// Process text file using StreamTokenizer Chapter 18 I/Oimport java.io.*;

public class ParsingTextFile{ // Main method public static void main(String[] args) { // Declare file reader and writer character (2 bytes) streams FileReader frs = null; FileWriter fws = null;

// Declare streamTokenizer StreamTokenizer in = null;


Patrick Healy

Class #15 – Input and Output ParsingTextFile.java (Demo)

// Declare a print stream PrintWriter out = null;

// For input file fields: student name, midterm1, // midterm2, and final exam score String sname = null; double midterm1 = 0; double midterm2 = 0; double finalScore = 0;

// Computed total score double total = 0;

try { // Create file input and output streams frs = new FileReader("grades.dat"); fws = new FileWriter("gradesout.dat");


Patrick Healy


// Create a stream tokenizer wrapping file input stream in = new StreamTokenizer(frs); out = new PrintWriter(fws); // Create PrintWriter object

// Read first token in.nextToken();

// Process a record // TTs are Tokenizer constants while (in.ttype != in.TT_EOF) // TT_EOF means end of file { // Get student name if (in.ttype == in.TT_WORD) // TT_WORD means token is a word sname = in.sval; else System.out.println("Bad file format");


Patrick Healy


// Get midterm1 if (in.nextToken() == in.TT_NUMBER) //TT_NUMBER means token is a number midterm1 = in.nval; else System.out.println("Bad file format");

// Get midterm2 score if (in.nextToken() == in.TT_NUMBER) midterm2 = in.nval; else System.out.println("Bad file format");

// Get final exam score if (in.nextToken() == in.TT_NUMBER) finalScore = in.nval;


Patrick Healy


total = midterm1*0.3 + midterm2*0.3 + finalScore*0.4; out.println(sname + " " + total);

in.nextToken( ); } } catch (FileNotFoundException ex) { System.out.println("Error: " + ex.getMessage()); System.out.println("File not found: in.dat"); } catch (IOException ex) { System.out.println(ex.getMessage()); }


Patrick Healy


finally // Always execute finally block { try { if (frs != null) frs.close(); if (fws != null) fws.close(); } catch (IOException ex) { System.out.println(ex); } } System.out.println("To view input file, TYPE GRADES.DAT"); System.out.println("To view output file, TYPE GRADESOUT.DAT"); } // End of main method} // End of class


Patrick Healy

Class #15 – Input and Output Chapter 18 Demo Programs

ReadBytes.java

WriteDemo.java

ShowFile.java

CopyFile.java CopyFileUsingByteStream.java

CompFile.java

RWData.java

RandomAccessDemo.java

PrintWriterDemo.java

ReadChars.java

ReadLines.java


Patrick Healy


TestDataStreams.java

TestFileClass.java

TestPrintWriters.java

ViewFile.java (cute file viewer program)

ParsingTextFile.java

TestRandomAccessFile.java needs these class files: AddressBook.java FixedLengthStringIO.class


Patrick Healy


TestDataStream.java

TestFileClass.java

TestFileReader.java

TestFileStream.java

TestFileWriter.java

TestObjectStreamForArray.java

TestObjectInputStream.java

TestObjectOutputStream.java

AddressBook.java (with FixedLengthStringIO.java)

Other created or required files: object.dat, temp.txt, student.dat


Patrick Healy

Class #15 – Input and Output End of Presentation

Itp 120 Chapt 19 2009 Binary Input & Output

Documents

new file

external file

nonexistent file

binary io classes

binary io text io

binary files data

file specific encoding

data io