事件派发线程SwingUtilitie的使用示例和invokeLater与invoikeAndWait的区别

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在Java中Swing是线程不安全的，是单线程的设计，这样的造成结果就是：只能从事件派发线程访问将要在屏幕上绘制的Swing组件。事件派发线程是调用paint和update等回调方法的线程，它还是事件监听器接口中定义的事件处理方法，例如，ActionListener中的actionPerformed方法在事件派发线程中调用。

　　Swing是事件驱动的，所以在回调函数中更新可见的GUI是很自然的事情，比如，有一个按钮被按下，项目列表需要更新时，则通常在与该按钮相关联的事件监听器的actionPerformed方法中来实现该列表的更新，从事件派发线程以外的线程中更新Swing组件是不正常的。

　　有时需要从事件派发线程以外的线程中更新Swing组件，例如，在actionPerformed中有很费时的操作，需要很长时间才能返回，按钮激活后需要很长时间才能看到更新的列表，按钮会长时间保持按下的状态只到actionPerformed返回，一般说来耗时的操作不应该在事件处理方法中执行，因为事件处理返回之前，其他事件是不能触发的，界面类似于卡住的状况，所以在独立的线程上执行比较耗时的操作可能更好，这会立即更新用户界面和释放事件派发线程去派发其他的事件。

　　SwingUtilities类提供了两个方法：invokeLate和invoteAndWait，它们都使事件派发线程上的可运行对象排队。当可运行对象排在事件派发队列的队首时，就调用其run方法。其效果是允许事件派发线程调用另一个线程中的任意一个代码块。

　　只有从事件派发线程才能更新组件

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1. import?java.awt.FlowLayout;??
2. import?java.awt.event.ActionEvent;??
3. import?java.awt.event.ActionListener;??
4. import?javax.swing.JButton;??
5. import?javax.swing.JFrame;??
6. import?javax.swing.JProgressBar;??
7. import?javax.swing.JTextField;??
8. public?class?SwingThreadTest1?extends?JFrame?{??
9. ????private?static?final?long?serialVersionUID?=?1L;??
10. ????private?static?final?String?STR?=?"Completed?:?";??
11. ????private?JProgressBar?progressBar?=?new?JProgressBar();??
12. ????private?JTextField?text?=?new?JTextField(10);??
13. ????private?JButton?start?=?new?JButton("Start");??
14. ????private?JButton?end?=?new?JButton("End");??
15. ????private?boolean?flag?=?false;??
16. ????private?int?count?=?0;??
17. ????public?SwingThreadTest1()?{??
18. ????????this.setLayout(new?FlowLayout());??
19. ????????add(progressBar);??
20. ????????text.setEditable(false);??
21. ????????add(text);??
22. ????????add(start);??
23. ????????add(end);??
24. ????????start.addActionListener(new?Start());??
25. ????????end.addActionListener(new?End());??
26. ????}??
27. ??????????
28. ????private?void?go()?{??
29. ????????while?(count?<?100)?{??
30. ????????????try?{??
31. ????????????????Thread.sleep(100);//这里比作要完成的某个耗时的工作??
32. ????????????}?catch?(InterruptedException?e)?{??
33. ????????????????e.printStackTrace();??
34. ????????????}??
35. ?????????????????????????//更新进度条和输入框??
36. ????????????if?(flag)?{??
37. ????????????????count++;??
38. ????????????????progressBar.setValue(count);??
39. ????????????????text.setText(STR?+?String.valueOf(count)?+?"%");??
40. ????????????}??
41. ????????}??
42. ????}??
43. ????private?class?Start?implements?ActionListener?{??
44. ????????public?void?actionPerformed(ActionEvent?e)?{??
45. ????????????flag?=?true;//设置开始更新的标志??
46. ????????????go();//开始工作??
47. ????????}??
48. ????}??
49. ????private?class?End?implements?ActionListener?{??
50. ????????public?void?actionPerformed(ActionEvent?e)?{??
51. ????????????flag?=?false;//停止??
52. ????????}??
53. ????}??
54. ????public?static?void?main(String[]?args)?{??
55. ????????SwingThreadTest1?fg?=?new?SwingThreadTest1();??
56. ????????fg.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);??
57. ????????fg.setSize(300,?100);??
58. ????????fg.setVisible(true);??
59. ????}??
60. }??

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progressBar.setValue(count);

text.setText(STR?+ String.valueOf(count) +?"%");

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1. import?java.awt.FlowLayout;??
2. import?java.awt.event.ActionEvent;??
3. import?java.awt.event.ActionListener;??
4. import?javax.swing.JButton;??
5. import?javax.swing.JFrame;??
6. import?javax.swing.JProgressBar;??
7. import?javax.swing.JTextField;??
8. public?class?SwingThreadTest2?extends?JFrame?{??
9. ????private?static?final?long?serialVersionUID?=?1L;??
10. ????private?static?final?String?STR?=?"Completed?:?";??
11. ????private?JProgressBar?progressBar?=?new?JProgressBar();??
12. ????private?JTextField?text?=?new?JTextField(10);??
13. ????private?JButton?start?=?new?JButton("Start");??
14. ????private?JButton?end?=?new?JButton("End");??
15. ????private?boolean?flag?=?false;??
16. ????private?int?count?=?0;??
17. ??????
18. ????GoThread?t?=?null;??
19. ????public?SwingThreadTest2()?{??
20. ????????this.setLayout(new?FlowLayout());??
21. ????????add(progressBar);??
22. ????????text.setEditable(false);??
23. ????????add(text);??
24. ????????add(start);??
25. ????????add(end);??
26. ????????start.addActionListener(new?Start());??
27. ????????end.addActionListener(new?End());??
28. ????}??
29. ????private?void?go()?{??
30. ????????while?(count?<?100)?{??
31. ????????????try?{??
32. ????????????????Thread.sleep(100);??
33. ????????????}?catch?(InterruptedException?e)?{??
34. ????????????????e.printStackTrace();??
35. ????????????}??
36. ????????????if?(flag)?{??
37. ????????????????count++;??
38. ????????????????System.out.println(count);??
39. ????????????????progressBar.setValue(count);??
40. ????????????????text.setText(STR?+?String.valueOf(count)?+?"%");??
41. ????????????}??
42. ????????}??
43. ????}??
44. ????private?class?Start?implements?ActionListener?{??
45. ????????public?void?actionPerformed(ActionEvent?e)?{??
46. ????????????flag?=?true;??
47. ????????????if(t?==?null){??
48. ????????????????t?=?new?GoThread();??
49. ????????????????t.start();??
50. ????????????}??
51. ????????}??
52. ????}??
53. ????//执行复杂工作，然后更新组件的线程??
54. ????class?GoThread?extends?Thread{??
55. ????????public?void?run()?{??
56. ????????????//do?something...??
57. ????????????go();??
58. ????????}??
59. ????}??
60. ????private?class?End?implements?ActionListener?{??
61. ????????public?void?actionPerformed(ActionEvent?e)?{??
62. ????????????flag?=?false;??
63. ????????}??
64. ????}??
65. ????public?static?void?main(String[]?args)?{??
66. ????????SwingThreadTest2?fg?=?new?SwingThreadTest2();??
67. ????????fg.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);??
68. ????????fg.setSize(300,?100);??
69. ????????fg.setVisible(true);??
70. ????}??
71. }??

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view plain

1. import?java.awt.FlowLayout;??
2. import?java.awt.event.ActionEvent;??
3. import?java.awt.event.ActionListener;??
4. import?javax.swing.JButton;??
5. import?javax.swing.JFrame;??
6. import?javax.swing.JProgressBar;??
7. import?javax.swing.JTextField;??
8. import?javax.swing.SwingUtilities;??
9. public?class?SwingThreadTest3?extends?JFrame?{??
10. ????private?static?final?long?serialVersionUID?=?1L;??
11. ????private?static?final?String?STR?=?"Completed?:?";??
12. ????private?JProgressBar?progressBar?=?new?JProgressBar();??
13. ????private?JTextField?text?=?new?JTextField(10);??
14. ????private?JButton?start?=?new?JButton("Start");??
15. ????private?JButton?end?=?new?JButton("End");??
16. ????private?boolean?flag?=?false;??
17. ????private?int?count?=?0;??
18. ??????
19. ????private?GoThread?t?=?null;??
20. ??????
21. ????private?Runnable?run?=?null;//更新组件的线程??
22. ????public?SwingThreadTest3()?{??
23. ????????this.setLayout(new?FlowLayout());??
24. ????????add(progressBar);??
25. ????????text.setEditable(false);??
26. ????????add(text);??
27. ????????add(start);??
28. ????????add(end);??
29. ????????start.addActionListener(new?Start());??
30. ????????end.addActionListener(new?End());??
31. ??????????
32. ????????run?=?new?Runnable(){//实例化更新组件的线程??
33. ????????????public?void?run()?{??
34. ????????????????progressBar.setValue(count);??
35. ????????????????text.setText(STR?+?String.valueOf(count)?+?"%");??
36. ????????????}??
37. ????????};??
38. ????}??
39. ????private?void?go()?{??
40. ????????while?(count?<?100)?{??
41. ????????????try?{??
42. ????????????????Thread.sleep(100);??
43. ????????????}?catch?(InterruptedException?e)?{??
44. ????????????????e.printStackTrace();??
45. ????????????}??
46. ????????????if?(flag)?{??
47. ????????????????count++;??
48. ????????????????SwingUtilities.invokeLater(run);//将对象排到事件派发线程的队列中??
49. ????????????}??
50. ????????}??
51. ????}??
52. ????private?class?Start?implements?ActionListener?{??
53. ????????public?void?actionPerformed(ActionEvent?e)?{??
54. ????????????flag?=?true;??
55. ????????????if(t?==?null){??
56. ????????????????t?=?new?GoThread();??
57. ????????????????t.start();??
58. ????????????}??
59. ????????}??
60. ????}??
61. ??????
62. ????class?GoThread?extends?Thread{??
63. ????????public?void?run()?{??
64. ????????????//do?something...??
65. ????????????go();??
66. ????????}??
67. ????}??
68. ????private?class?End?implements?ActionListener?{??
69. ????????public?void?actionPerformed(ActionEvent?e)?{??
70. ????????????flag?=?false;??
71. ????????}??
72. ????}??
73. ????public?static?void?main(String[]?args)?{??
74. ????????SwingThreadTest3?fg?=?new?SwingThreadTest3();??
75. ????????fg.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);??
76. ????????fg.setSize(300,?100);??
77. ????????fg.setVisible(true);??
78. ????}??
79. }??

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class GetInfoThread extends Thread {　Runnable getValue,setValue;　int value,currentValue;　public GetInfoThread(final Test applet){　getValue=new Runnable(){　public void run(){　　JProgressBar pb=applet.getProgressBar();　　currentValue=pb.getValue();　　}　};　setValue=new Runnable(){　　public void run(){　　JProgressBar pb=applet.getProgressBar();　　pb.setValue(value);　　}　}　}　public void run(){　　while(true){　　try{　　Thread.currentThead().sleep(500);　　value=(int)(Math.random()*100);　　try{　　SwingUtilities.invokeAndWait(getValue);//直到getValue可运行的run方法返回后才返回　　　}catch(Exception ex){　　　}　　　if(currentValue!=value){　　　SwingUtilities.invokeLater(setValue);　　　}　　}　　}catch(Exception ex){　　　}　　}　}

?invokeLater和invoikeAndWait的一个重要区别：可以从事件派发线程中调用invokeLater，却不能从事件派发线程中调用invokeAndWait，从事件派发线程调用invokeAndWait的问题是：invokeAndWait锁定调用它的线程，直到可运行对象从事件派发线程中派发出去并且该可运行的对象的run方法激活，如果从事件派发线程调用invoikeAndWait，则会发生死锁的状况，因为invokeAndWait正在等待事件派发，但是，由于是从事件派发线程中调用invokeAndWait，所以直到invokeAndWait返回后事件才能派发。

　　ex）actionPerformed();返回的时候事件派发线程才能派发线程，而在actionPerformed中使用invokeAndWait则会导致actionPerformed不能返回。所以也就无法派发invokeAndWait中的线程。

　　由于Swing是线程不安全的，所以，从事件派发线程之外的线程访问Swing组件是不安全的，SwingUtilities类提供这两种方法用于执行事件派发线程中的代码

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