/**

 * Simulates two particles flying apart in an explosion.

 *

 * @author TK Rogers

 * @version 7-28-11

 */

 

// Import statements add code to your programs from existing Java libraries

import java.awt.* ;

import javax.swing.* ;

import java.awt.event.ActionEvent ;

import java.awt.event.ActionListener ;

import javax.swing.Timer ;

public class BoomDemo extends JFrame implements ActionListener {

    int dotHeight = 6 ,

         dotWidth  = 6 ,

         x = 255 ,

         x_coordinate1 = 250 ,

         y_coordinate1 = 250 ,

         x_coordinate2 = 250 ,

         y_coordinate2 = 250 ;

       

    // The timer will create an event every 10 milliseconds. This

    // event will trigger the actionPerformed method and cause

    // the screen to repaint itself.

    private Timer timer = new Timer ( 10 , this ) ;

 

     // Note: methods are small segments of code that perform specific tasks.

   // Methods can be reused repeatedly within a program.

       

    // The method below is called a constructor and must have the same

   // name as the class. Constructors set initial conditions.    

   BoomDemo ( ) {

       setSize ( 500, 500 ) ; // sets the size of the frame

       timer.start ( ) ;

   }

       

    // The main method starts up the program.  

    public static void main ( ) {

        BoomDemo boom = new BoomDemo ( ) ;

        boom.setVisible ( true ) ;

        boom.setBackground( new Color ( 255, 255, 255 ) ) ;

    }

       

   // The paint method automatically runs once. Afterwards it can

   // only be run using the repaint method.

   public void paint ( Graphics g ) {

        // In Java graphics, the origin is at the top left. increasing

        // the x-coordinate moves objects to the right. Increasing the 

        // y-coordinate moves objects downward.

      

        if ( x_coordinate1 == 500) {

            x_coordinate1 = 250 ;

            y_coordinate1 = 250 ;

            x_coordinate2 = 250 ;

            y_coordinate2 = 250 ;

            x = 255 ;

        }

      

        // The next 2 lines of code paint over, hence, erase any dots drawn the

        // previous time repaint ( ) was run       

        g.setColor ( new Color ( x, x, x ) ) ;

        g.fillRect ( 0, 0, getSize ( ).width, getSize ( ).height ) ;

        

        g.setColor ( new Color ( 255, 0, 0 ) ) ;

        g.fillOval ( x_coordinate1, y_coordinate1, dotHeight, dotWidth ) ;

    // The next 2 lines of code cause the red dot to move along a 

  // diagonal line, downward and toward the right, away from the

  // center.

        x_coordinate1++ ; // The ++ operator adds 1 to x_Coordinate

        y_coordinate1 = x_coordinate1 ; // This is the Java version of the

  // equation y = mx + b where m or the slope = 1 and b = 0

           

        g.setColor (new Color ( 0, 0, 255 ) ) ;

        g.fillOval ( x_coordinate2, y_coordinate2, dotHeight, dotWidth )

  // The next 2 lines of code cause the blue dot to move along a

  // diagonal line, upward and toward the left away, from the center.

        x_coordinate2-- ; // The -- operator subtracts 1 from x_Coordinate

        y_coordinate2 = x_coordinate2 ;

        x-- ;

    }

   

    // The below method is called every time the timer object creates an

    // event. The method is a "listener". It listens for events and when

    // they occur,takes appropriate actions.

    public void actionPerformed ( ActionEvent e ) {

             repaint ( ) ; // Reruns the paint method.

    }

}