16.12

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class Test_16_12 extends JFrame{
    
    public Test_16_12(){
        add(new JP());
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Test_16_12 t1 = new Test_16_12();
        t1.setTitle("Test_16.12");
        t1.setLocationRelativeTo(null);
        t1.setSize(300,300);
        t1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        t1.setVisible(true);
    }
    
    static class JP extends JPanel{
        private int h =0;
        public JP(){
        Timer timer = new Timer(10,new TimerListener());
        timer.start();
        }
        public void paintComponent(Graphics g){
            super.paintComponent(g);
            
            int xCenter = getWidth()/2;
            int yCenter = getHeight()/2;
            int radius = (int)(Math.min(getWidth(), getHeight())*0.4);
            int x = xCenter - radius;
            int y = yCenter - radius;
            
            
            g.fillArc(x, y, 2*radius, 2*radius, 0+h, 30);
            g.fillArc(x, y, 2*radius, 2*radius, 90+h, 30);
            g.fillArc(x, y, 2*radius, 2*radius, 180+h, 30);
            g.fillArc(x, y, 2*radius, 2*radius, 270+h, 30);            
        }
        class TimerListener implements ActionListener
        {                
            @Override
            public void actionPerformed(ActionEvent arg0) {
                // TODO Auto-generated method stub
                h += 3;
                repaint();
            }
        }
    }
}

需要注意的： Timer的创建应该放在JP的构造函数中

效果图：下图实际上是动态的