Where does a Java application start?

A Java application is composed of 1 or more classes. When the Java run-time interpreter is instructed to begin executing a Java application, it must be provided with a class that contains a method called 'main'. The first statement to be executed for a Java application is the first statement inside this main class's method main.

A main method is show in full in the abbreviated version of the BallWorld class below:

// BallWorld.java

import java.awt.*;

public class BallWorld extends Frame

{

  private Ball myBall;

  static public void main (String [] args)

{

  BallWorld world = new BallWorld ();

  world.show ();

}

private BallWorld ()

{ // implementation of BallWorld constructor class }

public void paint(Graphics g)

{ // implementation of paint method }

private void pause(int numMilliseconds)

{ // implementation of pause method }

} // class BallWorld

BallWorld world = new BallWorld ();

Although all classes that comprise an  application need to be compiled, we only tell the interpreter the name of the main  class. The class Ball does not contain the method main, it is used by BallWorld. We can using Kawa run the BallWorld class.