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It can execute a prerecorded list of instructions (a program).
Chapter 1 Java: an Introduction to Computer Science & Programming - Walter Savitch 2
Computer Basics
Computer system:
hardware + software
Hardware: the physical
components
Software: the
instructions that tell the
hardware what to do
Chapter 1 Java: an Introduction to Computer Science & Programming - Walter Savitch 8
Running a Program
Program
ComputerData
(input for the program)Output
Computing has been around for millennia
1835 – Charles Babbage first used punch cards to “program” his analytic engine
• Pre 1940 - Analog Computers
• 1940 – First electric digital computers
http://en.wikipedia.org/wiki/History_of_computers
Machine language
Assembly language
1945 - Plankalkül (Konrad Zuse)
1954 - FORTRAN
1958 - LISP
1958 - ALGOL
1959 - COBOL
1962 - APL
1962 - Simula
1964 - BASIC
1964 - PL/I
1970 - Pascal
1972 - C
1972 - Smalltalk
1972 - Prolog
1973 - ML
1978 - SQL
1983 - Ada
1983 - C++
1985 - Eiffel
1987 - Perl
1989 - FL (Backus)
1990 - Haskell
1990 - Python
1991 - Java
1993 - Ruby
2000 - C#
So Many Languages...
People understand
words, symbols,
and pictures.
Computers can
only execute 1’s
and 0’s
People need to
write in 1’s and
0’s
Computers
understand words.
People write
program in words
Program is
translated into
1’s and 0’s
Now the
computer can
execute the
program
Compiler
Translates
words
Get and
executable
Translate high-level language to machine language
Source code
The original program in a high level language
Object code
The translated version in machine language
Slide 1- 11
Invention of a Compiler
Grace Hopper
Admiral Grace Hopper was a “mathematician,
computer scientist, social scientist, corporate politician,
marketing whiz, systems designer,
and programmer,”
In 1953 she invented the compiler, the
intermediate program that translates English
language instructions into the language of the
target computer.
She did this, she said, because she was “lazy”
and hoped that “the programmer may return to
being a mathematician.”
The First Digital Programmers
The Evolution of Programming
1001 0110 1001 1001 0110
1001 1011 1011 1111 0000
1010 1110 1101 1010 1010
Programming in Binary
0
100
200
300
400
500
600
700
800
900
1000
Hardness Level Number of
programmers who
could program
with it
Effeciency of
creating a
program
The Evolution of Programming
int BDISK_INT
mov si,seg DGROUP ;
mov ds,si ;
mov si,offset err_write ;
jc ErrorExit ;
mov si,offset
msg_ok ;
Programming in Assembly Language
0
100
200
300
400
500
600
700
800
900
1000
Hardness Level Number of
programmers who
could program with
it
Effeciency of
creating a program
The Evolution of Programming
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h> /* sleep() */
#include <time.h>
int main(void) {
time_t start, end;
start = time(NULL);
if(start == (time_t)-1) {
fprintf(stderr, "Error: `time()'\n");
return 1;
}
printf("sleepingggzzzzzzz....5sec's\n");
sleep(5);
end = time(NULL);
printf("according to difftime(), slept for %.2f sec's\n", difftime(end, start));
return 0;
}
Programming in High-Level Language
0
100
200
300
400
500
600
700
800
900
1000
Hardness Level Number of
programmers who
could program with
it
Effeciency of
creating a program
The Evolution of Programming
/** * This program prints out all its
command-line arguments. **/
public class Echo {
public static void main(String[] args) {
int i = 0; // Initialize the loop variable
while(i < args.length) {
// Loop until we reach end of array
System.out.print(args[i] + " ");
// Print each argument out
i++;
// Increment the loop variable
}
System.out.println( );
// Terminate the line
}
}
Programming in High-Level Language with OOD
0
100
200
300
400
500
600
700
800
900
1000
Hardness Level Number of
programmers who
could program with
it
Effeciency of
creating a program
Did not want to use C because of its lack of security, garbage collection, portability, and threading.
James Gosling, Arthur Van Hoff, and Andy Bechtolsheim, or Just Another Vague Acronym
first 4 bytes (the so-called "Magic number") of any class file are, in hexadecimal, 0xCAFEBABE
Why Java?
Object Oriented – Allows one to reuse code...yeah! you do not have to write the same code twice.
Garbage Collection - When no references to an object remain, the Java garbage collector automatically deletes the object, freeing memory and preventing a memory leak...yeah! no more slow running programs that make your computer crash!
Platform Independent - programs written in the Java language must run similarly on diverse hardware...yeah! now those with Macs and Linux could also use your programs.
JAVA
6.5 million developers
Java powers more than 4.5 billion devices including:
800+ million PCs
2.1 billion mobile phones and other handheld devices (source: Ovum)
3.5 billion smart cards
Set-top boxes, printers, Web cams, games, car navigation systems, lottery terminals, medical devices, parking payment stations, and more.
SDK
A SDK is short for Software Development Kit.
A SDK it used to create a new programs.
A SDK is given out by the people who create the program language.
A SDK is updated, improved upon, and grows in size as time goes on.
JAVA SDK aka JDK
Java 1.02
250 classes
Slow
Cute name and logo, fun to use, lots of bugs, and applets are the big thing
Java 1.1
500 classes
A little faster
More capable, friendlier. Becoming very popular. Better GUI code.
Java 2
(versions 1.2 – 1.4)
2300 classes
Much faster
Can run at native speeds. Serious and powerful. Comes in 3 flavors: Micro Edition (J2ME), Standard Edition (J2SE), and Enterprise Edition (J2EE). Becomes the language of choice for new enterprise and mobile applications.
Java 5.0
(versions 1.5 -1.5.0_18)
3500 classes
More Powerful and easier to Develop.
Java 5.0 or “Tiger” added major changes to the language itself, making it easier for programmers and giving new features that were popular in other languages.
Java 7 or “Dolphin”
Planned release in 2010
improved multithreading capabilities to take advantage of multi-processors
Java 6
(Update 10-21)
5000 classes
More Support of Graphics.
Better start up time, and an attempt to improve applets by adding JavaScript and making them AJAX applications.
JAVA SDK
Download it from java.com of java.sun.com
Download the latest non-beta version
Java SDK
Contains a compiler – takes your code and makes it into an executable
Contains a number of libraries of pre-written code that you can use in your programs...Yeah!
DOES NOT contain a text editor or IDE that you can use to write your programs.
You can not see it in “All Programs” on your computer.
JAVA SDK
In order to use it/test it you must run it from a command line.
Later we will see how to call the Java SDK functions that we make on the command line via a simple IDE.
Textpad
Notepad++
• Most high-level languages need a different
compiler for each type of computer and for
each operating system.
• Most compilers are very large programs that
are expensive to produce.
Compilers
• A compiler translates a program
from a high-level language to a
low-level language the computer
can run.
• You compile a program by
running the compiler on the high-
level-language version of the
program called the source
program.
Compilers
• Compilers produce machine- or assembly-
language programs called object programs.
• Most high-level languages need a different compiler
for each type of computer and for each operating
system.
• Most compilers are very large programs that are
expensive to produce.
Compilers, cont.
Source Code
Compiler
Executable
Mac PC Other
Source Code
Compiler
Executable
Source Code
Compiler
Executable
• The Java compiler does not translate a Java
program into assembly language or machine
language for a particular computer.
• Instead, it translates a Java program into
byte-code.
– Byte-code is the machine language for a
hypothetical computer (or interpreter) called the
Java Virtual Machine.
Java Byte-Code
JVM
Source Code
Executable
Mac PC Other
Compiler
Executable
Byte Code
Executable
Mac - JVM
PC - JVM Other - JVM
• The Java compiler does not translate a Java
program into assembly language or machine
language for a particular computer.
• Instead, it translates a Java program into
byte-code.
– Byte-code is the machine language for a
hypothetical computer (or interpreter) called the
Java Virtual Machine.
Java Byte-Code
• After compiling a Java program into byte-
code, that byte-code can be used on any
computer with a byte-code interpreter and
without a need to recompile.
• Byte-code can be sent over the Internet and
used anywhere in the world.
• This makes Java suitable for Internet
applications.
Portability
Byte Code
Java Program
Java is better than other programming code
because…
it is platform independent.
the interpreter is smaller than a full compiler.
Needed
•JDK
•Text Editor
•Command Line
Steps
•Create a source file
•Compile it to a .class
•Run the Program
Chapter 1 Java: an Introduction to Computer Science & Programming - Walter Savitch 31
A Sample Java Program
public class FirstProgram
{
public static void main(String[] args)
{
System.out.println("Hello out there.");
System.out.println("Want to talk some more?");
System.out.println("Answer y for yes or n for no.");
char answerLetter;
answerLetter = SavitchIn.readLineNonwhiteChar();
if (answerLetter == 'y')
System.out.println("Nice weather we are having.");
System.out.println("Good-bye.");
System.out.println("Press enter key to end program.");
String junk;
junk = SavitchIn.readLine();
}
}
IDE
A Integrated Development Environment
Used to help in the creation, compilation, and running of your Java programs.
Different levels of IDE’s.
TextPad NetBeans
TextPad or Notepad++
How to use TextPad and Notepad++
How to Download Java, NotePad++, and TextPad so that you can create JAVA Programs on your own.
Help is Out There
There are 6.5 million users of JAVA
Many of these users need a lot of assistance
There are hundreds of forums out on the Web that have programmers that like to help.
Many beginning JAVA programmer forums
javaranch.com
java.sun.com
java.com
grammatical mistakes in a program
the grammatical rules for writing a program are very strict
The compiler catches syntax errors and prints an error message.
example: using a period where a program expects a comma
errors that are detected when
your program is running, but
not during compilation
When the computer detects an
error, it terminates the program
an prints an error message.
example: attempting to divide
by 0
errors that are not detected during compilation
or while running, but which cause the program
to produce incorrect results
example: an attempt to calculate a Fahrenheit
temperature from a Celsius temperature by
multiplying by 9/5 and adding 23 instead of 32
http://java.sun.com/nav/used/
http://javaboutique.internet.com/applications/
Chapter 1 Java: an Introduction to Computer Science & Programming - Walter Savitch 38
Good Programming Practice:Identifier Naming Conventions
Always use meaningful names, e.g. finalExamScore, instead of something like x, or
even just score.
Use only letters and digits.
Capitalize interior words in multi-word names, e.g. answerLetter.
Names of classes start with an uppercase letter.
» every program in Java is a class as well as a program.
Names of variables, objects, and methods start with a
lowercase letter.
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