Introduction to programming in java
Introduction to programming in java. [email protected] Input and output to screen with Java program Structure of Java programs Statements Conditional statements.
Mar 28, 2015
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Introduction to programming in java
• Input and output to screen with Java program
• Structure of Java programs
• Statements
• Conditional statements
• Loop constructs
• Arrays, character and string handling
• Functions
Syllabus
• Structure of Java programs
• Input and output to screen with Java program
• Statements (what is a statement)
Lecture Outcomes
Books & References
Introduction to Java and Object Oriented Programming (Volume 1)
1.Chapter 2.After todays Lecture you should be able to complete all exercisesIn Section 2.10, page 14.
2.Chapter 3If you are confident with all the material in Chapter 2, then start Reading Chapter 3.
3.Extra More practise exercises are on page:
http://introcs.cs.princeton.edu/java/11hello/
• Structure of Java programs
• Compiling and running the program
• Printing messages to the screen
Contents for Today’s Lecture
Some Basics
Definition of a program?A sequence of instructions that a computer can interpret and execute.
Why don’t we just use natural languages such as English?A computer is not intelligent enough to understand natural languages.
class class-name {
public static void main(String args[]) {
statement1;
statement2;
…
…
}
}
Structure of Java Programs“class-name.java”
8
A statement written in Java
println(“Hello World!");
String hello = “Hello World!";
println(hello);
every statement isterminated with a ;
“First.java”
Public class First {
public static void main(String args[]) {
System.out.println(“Hello World”);
}
}
Example Program
statement
10
Creating and Compiling Programs
• On command line– javac file.java
Source Code
Create/Modify Source Code
Compile Source Code i.e. javac Welcome.java
Bytecode
Run Byteode i.e. java Welcome
Result
If compilation errors
If runtime errors or incorrect result
11
Executing Applications
• On command line– java classname
JavaInterpreter
on Windows
JavaInterpreter
on Sun Solaris
JavaInterpreteron Linux
Bytecode
...
12
Examplejavac Welcome.java
java Welcome
output:...
Compile and run java command line
Compile javac file-name.java
Run java filename
Compile javac HelloWorld.java
Run java HelloWorld
Example: HelloWorld.java
Compiling: is the process of translating source code written in a particular programming language into computer-readable machine code that can be executed.
$ javac First.java
This command will produce a file ‘First.class’, which is used for running the program with the command ‘java’.
Running: is the process of executing program on a computer.
$ java First
Compiling & Running the Program
“second.java”
class second {
public static void main(String args[]) {
System.out.println(“Hello World”);
}
}
Example Program
Compile javac second.java
Run java second
“HelloWorld.java”
class HelloWorld{
public static void main(String args[]) {
System.out.println(“Hello World”);
}
}
Example Program
Compile javac HelloWorld.java
Run java HelloWorld
1. HelloWorld java
2. Welcome.java
3. Myname.java
4. MyDate ofBirth.java
Compile Run a few example using Command line
1. System.out.println(“Hello World”); – outputs the string “Hello World” followed by a new line on the screen.
2. System.out.print(“Hello World”); - outputs the string “Hello World” on the screen. This string is not followed by a new line.
3. Some Escape Sequence –
• \n – stands for new line character
• \t – stands for tab character
About Printing on the Screen
19
Java print() and println()
• Text can be printed on the screen using print() or println().
• Using println() puts a new line at the end of the text. print("7*3"); println("="); println(7*3); This code prints: 7*3= 21
ExampleWelcome.java
public class Welcome
{
public static void main(String args[])
{
System.out.print("Welcome ");System.out.println("to");System.out.println(“java!");
}
}
}
}Welcome to java!Output
ExampleWelcome3.java ( includes \n and \t)
public class Welcome
{
public static void main(String args[])
{
System.out.print("Welcome \n ");System.out.print("to \t");System.out.println(“java!");
}
}
}
}Welcome to java!Output
• Some common errors in the initial phase of learning programming:
- Mismatch of parentheses
- Missing ‘;’ at the end of statement
- Case sensitivity
• Writing programs on your own is the best way to learn how to program.
Some Tips About Programming
23
Comments in java
• There are two ways of commenting code.• Comments starting with // and terminated by end of line// Lahcen Ouarbya
// 1 October 2012
// Hello World• Comments enclosed in /* *//* Lahcen Ouarbya
1 October 2012
Hello World
*/
good to make severallines of comments standout in your program
24
Concatenating output with +
print("I like programming in ");println("Java");
This code prints: I like programming in Java
print("I like programming in “ + “Java” );
This code prints: I like programming in Java
println(“ square root of 4 = " 2 + " or " -2);
This code prints: square root of 4 = 2 or -2
ExampleConcatenate.java
public class Concatenate
{
public static void main(String args[])
{ System.out.print("I like programming in "); System.out.println(“java"); System.out.println("I like programming in “ + “java”); System.out.println(“ square root of 4 = “+ 2 + " or “ + -2);
}
{
}
}I like programming in javaI like programming in javasquare root of 4 = 2 or -2Output
ExampleWelcome.java
public class Welcome
{
public static void main(String args[])
{
System.out.print("Welcome ");System.out.print("to ");System.out.println("Java!");
System.out.println(“Welcome “ + "to “+ " Java!");
}
}
}
}
Welcome to java!Welcome to java!Output
1. Write a program which prints the following information about at least 5 persons:
`Full Name ‘ `Email-Address’ ` Telephone Number’
use print and println and see the difference.
2. Write a program that prints the time table of 5 and time table of 9. (you will need to use concatenation.)
Some Assignments
EndUsing Command line Arguments
public class TestMain
{
public static void main(String args[])
{
. . .
}
}
java TestMain arg0 arg1 arg2 … argn
}
}
Processing Command-Line Parameters
The main method, get the arguments from
args[0], args[1], ..., args[n]
arg0, arg1, ..., argn
}
}
ExampleArgument.java
public class Welcome
{
public static void main(String args[])
{
System.out.print("Hi, "); System.out.print(args[0] + " " ); System.out.println(". How are you?");
}
}
}
} Hi, Lahcen. How are you?
Java Argument Lahcen
ExampleArgument1.java
public class Argument1
{
public static void main(String args[])
{
System.out.print("Hi, "); System.out.print(args[0] + " " ); System.out.print(args[1] + " " ); System.out.println(". How are you?");
}
}
}
}Hi, java programs. How are you?
Java Argument java programs
ExampleArgument2.java
public class Argument2
{
public static void main(String args[])
{
System.out.print("Hi, “+ args[0] + “ ”args[1] + (". How are you?");
}
}
}
}
Hi, java programs. How are you?
Java Argument java programs
summary
• HelloWorld.java• Compile and run java programms.• print/println• “\n” new line• “\t” tab• Concatenation• Use of Arguments.
More practice exercises.
Introduction to Java and Object Oriented Programming (Volume 1)
1.Chapter 2.After todays Lecture you should be able to complete all exercisesIn Section 2.10, page 14.
2.Chapter 3If you are confident with all the material in Chapter 2, then start Reading Chapter 3.
3.Extra More practise exercises are on page:
http://introcs.cs.princeton.edu/java/11hello/
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