Java中Swing組件上繪圖機制舉例

A program which demonstrates the basic paint mechanism for Swing components (JPanel for example).

1. package com.han;
3. import java.awt.*;
4. import java.awt.event.*;
5. import javax.swing.*;
7. /**
8. * A program which demonstrates the basic paint mechanism for Swing components
9. * (JPanel for example).
10. * @author han
11. *
12. */
13. public class SwingPaintDemo {
14. public static void main(String[] args) {
15. JFrame f = new JFrame("Aim For the Center");
16. f.addWindowListener(new WindowAdapter() {
17. public void windowClosing(WindowEvent e) {
18. System.exit(0);
19. }
20. });
21. JPanel panel = new BullsEyePanel();
22. panel.add(new JLabel("BullsEye!", SwingConstants.CENTER), BorderLayout.CENTER);
23. f.getContentPane().add(panel, BorderLayout.CENTER);
24. f.pack();
25. f.setVisible(true);
26. }
27. }
29. /**
30. * A Swing container that renders a bullseye background
31. * where the area around the bullseye is transparent.
32. */
33. @SuppressWarnings("serial")
34. class BullsEyePanel extends JPanel {
36. public BullsEyePanel() {
37. super();
38. setOpaque(false); // we don't paint all our bits
39. setLayout(new BorderLayout());
40. setBorder(BorderFactory.createLineBorder(Color.black));
41. }
42. @Override
43. public Dimension getPreferredSize() {
44. // Figure out what the layout manager needs and
45. // then add 100 to the largest of the dimensions
46. // in order to enforce a 'round' bullseye
47. /* the use of "super." is very important,
48. because otherwise the JRE will throw a StackOverflowError.
49. And because of the JFrame.pack() used above,
50. the JFrame window will be resized to adapter the Container size.*/
51. Dimension layoutSize = super.getPreferredSize();
52. int max = Math.max(layoutSize.width,layoutSize.height);
53. return new Dimension(max+100,max+100);
54. }
56. @Override
57. protected void paintComponent(Graphics g) {
58. Dimension size = getSize();
59. System.out.println(size.width);
60. System.out.println(size.height);
61. int x = 0;
62. int y = 0;
63. int i = 0;
64. while(x < size.width && y < size.height) {
65. g.setColor(i%2==0? Color.red : Color.white);
66. g.fillOval(x,y,size.width-(2*x),size.height-(2*y));
67. x+=10; y+=10; i++;
68. }
69. }
70. }