java Swing 按钮不显示、鼠标滑过才显示

万蕊科技

1. import javax.swing.*;
   
2. 
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3. import java.awt.*;
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4. import java.awt.event.*;
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5. import java.awt.image.ImageObserver;
   
6. 
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7. public class Welcome extends JFrame{
   
8. /**
   
9. *
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10. */
    
11. private static final long serialVersionUID = 1L;
    
12. /**
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13. *
    
14. */
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15. private JButton JB,JB1,JB2,JB3;
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16. private JLabel JL;
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17. private Image img;
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18. private Toolkit tool;
    
19. 
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20. Welcome(){
    
21. super("欢迎来到科帮网");
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22. setSize(600,500);
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23. setLocation(250, 150);
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24. Container container = getContentPane();
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25. tool = getToolkit();
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26. container.setLayout(null);
    
27. 
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28. JB = new JButton("查询学校景点信息");
    
29. JB1 = new JButton("查询2景点间的最短距离");
    
30. JB2 = new JButton("查询旅游路线");
    
31. JB3 = new JButton("退出");
    
32. JL = new JLabel("欢迎使用校园导游咨询系统");
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33. img = tool.getImage("E://School.jpg");
    
34. 
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35. JB.addActionListener(new MyMonitor());
    
36. JB1.addActionListener(new MyMonitor());
    
37. JB2.addActionListener(new MyMonitor());
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38. JB3.addActionListener((new MyMonitor()));
    
39. 
    
40. JL.setBounds(180, 20, 300, 40);
    
41. JB.setBounds(200, 60, 200, 30);
    
42. JB1.setBounds(200, 100, 200, 30);
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43. JB2.setBounds(200, 140,200, 30);
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44. JB3.setBounds(500, 400, 90, 30);
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45. 
    
46. 
    
47. container.add(JB);
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48. container.add(JB1);
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49. container.add(JB2);
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50. container.add(JB3);
    
51. container.add(JL);
    
52. 
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53. setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
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54. setVisible(true);
    
55. 
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56. }
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57. 
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58. private class MyMonitor implements ActionListener{
    
59. 
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60. public void actionPerformed(ActionEvent e) {
    
61. if(e.getSource()==JB){
    
62. new MyGraphy();
    
63. setVisible(false);
    
64. }
    
65. if(e.getSource()==JB1){
    
66. new ShowLength();
    
67. setVisible(false);
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68. }
    
69. if(e.getSource()==JB2){
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70. new ShowView();
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71. setVisible(false);
    
72. }
    
73. 
    
74. if(e.getSource()==JB3){
    
75. System.exit(0);
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76. }
    
77. 
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78. }
    
79. 
    
80. }
    
81. 
    
82. public void paint(Graphics g){
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83. g.drawImage(img, 100, 230, 400, 250, (ImageObserver) this);
    
84. 
    
85. }
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86. 
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87. 
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88. public static void main(String[] args) {
    
89. new Welcome();
    
90. }
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91. }
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复制代码

原因：paint方法被你重写了，但是你没处理好、所以要在 paint 方法前加super.paint(g)