Thursday, 15 November 2007

Hello world!

Hey guys,

Today I will teach you how to write your first program in Java, compile it, and then decompile with jad.

Open your favourite text editor, and type (or copy&paste) the following code:
public class Hello {

public static void main(String[] args) {

System.out.println("Hello world!");


Save the code as, and open a console window. Navigate to the directory where you saved the file and execute the following command to compile the program:
Hopefully the program will be compiled without any errors. You'll notice that another file named Hello.class will be created in the same directory. To run it, type the following command:
java Hello
Of course, the program will run and output "Hello world!" :)

Congratulations, you have successfully written, compiled and executed your first Java program. It is very simple, but probably you can use it as a template for other programs in the future.

Now it's time to decompile it and see how the code looks like. From the console, type
jad Hello.class
A new file named Hello.jad will be created. Have a look at it
// Decompiled by Jad v1.5.8f. Copyright 2001 Pavel Kouznetsov.
// Jad home page:
// Decompiler options: packimports(3)
// Source File Name:


public class Hello

public Hello()

public static void main(String args[])
System.out.println("Hello world!");
Almost the same as the original code. Cool huh? :)

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