rollingball.java

用java编写的滚动的小球的代码 能看得出是个小球在滚动

A rolling ball

import javax.swing.*; 
import java.awt.*; 
import java.awt.geom.*; 

class RollingBall extends JPanel { 
    Ellipse2D.Float ball = new Ellipse2D.Float( -100, 100, 50, 50 ); 

    public void paintComponent( Graphics g ) { 
        super.paintComponent( g ); 
        Graphics2D g2 = ( Graphics2D ) g; 

        // Draw the ball 
        g2.fill( ball ); 
        // Draw the rotating ellipse by skewing the Device Space 
        double angdeg =     // One rotation per ball's travelling over its perimeter 
            ball.x++ % ( Math.PI * ball.width ) / ( Math.PI * ball.width ) * 360; 
        g2.rotate( Math.toRadians( angdeg ), ball.getCenterX( ), ball.getCenterY( ) ); 
        g2.scale( .5, 1 ); 
        g2.translate( ball.getCenterX( ), 0 ); 
        g2.setColor( Color.gray ); 
        g2.fill( ball ); 
    } 

    public void roll( ) throws Exception { 
        while( true ) { 
            repaint( ); 
            Thread.sleep( 8 ); 
        } 
    } 

    public static void main( String[ ] args ) throws Exception { 
        JFrame f = new JFrame( ); 
        RollingBall rb = new RollingBall( ); 

        f.setSize( 999, 185 ); 
        f.getContentPane( ).add( rb ); 
        f.setVisible( true ); 
        rb.roll( ); 
    } 
}