2- Java Programming Introduction

7/29/2019 2- Java Programming Introduction

1/24

Java Programming

Introduction

Muhammad Haris

Lecturer GIS Center, PUCIT


2/24

Muhammad Haris - Lecturer GISCenter PUCIT 2

A Simple Java Program

//This program prints Welcome to Java!

public class Welcome {

public static void main(String[] args) {System.out.println("Welcome to Java!");

}

}


3/24


Creating and Editing Using NotePad


4/24


Creating, Compiling, and Running

Programs

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


public static void main(String[] args) {

System.out.println("Welcome to Java!");}

}

Method Welcome()

0 aload_0

Method void main(java.lang.String[])

0 getstatic #2

3 ldc #3 5 invokevirtual #4

Saved on the disk

stored on the disk

Source code (developed by the programmer)

Byte code (generated by the compiler for JVMto read and interpret, not for you to understand)


5/24





}

}

Trace a Program Execution

Enter main method


6/24





}

}


Execute statement


7/24





}

}


print a message to the

console


8/24


Compiling and Running Java from

the Command Window

1. Set path to JDK bin directory

set path=c:\Program Files\java\jdk1.5.0\bin

2. Compile

javac Welcome.java

3. Run

java Welcome


9/24


Demonstration


10/24


Anatomy of a Java Program

Comments Reserved words

Modifiers

Statements

Blocks

Classes

Methods

The main method



public static void main(String[] args)

{

System.out.println("Welcome to

Java!");

}

}


11/24


Comments

In Java, comments are preceded by two slashes (//) in

a line, or enclosed between /* and */ in one or multiple

lines. When the compiler sees //, it ignores all text after

// in the same line. When it sees /*, it scans for the next*/ and ignores any text between /* and */.


12/24


Reserved Words

Reserved words or keywords are words that have a

specific meaning to the compiler and cannot be used

for other purposes in the program.

For example, when the compiler sees the word class, it

understands that the word after class is the name for

the class. Other reserved words in the program are

public, static, and void. Their use will be introducedlater in the book.


13/24


Modifiers

Java uses certain reserved words calledmodifiers that specify the properties of the data,methods, and classes and how they can beused.

Examples of modifiers are public and static.Other modifiers are private, final, abstract, andprotected.

A public data, method, or class can be accessed

by other programs. A private data or methodcannot be accessed by other programs.


14/24


Statements

A statement represents an action or a sequence ofactions. The statement

System.out.println("Welcome to Java!")

in the program is a statement to display the greeting"Welcome to Java!" Every statement in Java ends with

a semicolon (;).


15/24


Blocks

A pair of braces in a program forms a block that groups

components of a program.

public class Test {


System.out.println("Welcome to Java!");

}

}

Class block

Method block


16/24


Classes

The class is the essential Java construct.A class is a template or blueprint for objects.

Note: The mystery of the class will continue to be unveiledthroughout this course. For now, though, understand that a program

is defined by using one or more classes.


17/24


Methods

What is System.out.println? It is a method: acollection of statements that performs a sequenceof operations to display a message on the console.

It can be used even without fully understanding thedetails of how it works.


18/24


Method

It is used by invoking a statement with a string argument.System.out.println("Welcome to Java!");

The string argument is enclosed within

Parentheses( ). In this case, the argument is

"Welcome to Java!"

You can call the same println method with a differentargument to print a different message.

System.out.println("Welcome to GIS!");


19/24


main Method

The main method provides the control of program flow.

The Java interpreter executes the application by

invoking the main method.

The main method looks like this:


// Statements;

}


20/24


Displaying Text in a Message Dialog

Box

you can use the showMessageDialog method in

the JOptionPane class.

JOptionPane is one of the many predefinedclasses in the Java system, which can be reused

rather than reinventing the wheel.


21/24


The showMessageDialog Method

JOptionPane.showMessageDialog(null,"Welcome to Java!",

Display Message",

JOptionPane.INFORMATION_MESSAGE));


22/24

Complete Program

import javax.swing.JOptionPane;



System.out.println("Welcome to Java!");JOptionPane.showMessageDialog(null, "Welcome to Java!", "Display

Message",JOptionPane.INFORMATION_MESSAGE);

}

}



23/24

2 Ways of Input Output

Input:

System.out.println("Enter your name");

Scanner scanner = new Scanner(System.in);

String input = scanner.nextLine();

Output:System.out.println("Welcome " + input);

Input:

String input = JOptionPane.showInputDialog("Enter your name");

Output:

JOptionPane.showMessageDialog (null, "Welcome " + input );



24/24


Assignment

Read Next Slide

Variables and Identifiers

2- Java Programming Introduction

Documents

Transcript of 2- Java Programming Introduction