适配器类是抽象类 抽象类不是不能建立对象吗??
但是这句话怎么理解啊
WindowAdapter wa = new WindowAdapter();
上面这句是错误的  提示抽象类不能创建对象这个倒是理解
但是下面这句
WindowAdapter wa = new WindowAdapter(){};
这句话居然没错 这是什么意思???创建WindowAdapter的对象??空参构造??? 对这句话不理解  谁能告诉我??

WindowAdapter源代码贴这里了，来，围观一下！
哎，，，，
说起源代码
心情很是复杂啊
想起了我的英语老师
为什么老师对我那么好
我却还是没把英语学好呢
{:soso_e118:}{:soso_e117:}{:soso_e131:}{:soso_e113:}{:soso_e132:}{:soso_e130:}{:soso_e122:}{:soso_e130:}

1. package java.awt.event;
   
2. 
   
3. /**
   
4. * An abstract adapter class for receiving window events.
   
5. * The methods in this class are empty. This class exists as
   
6. * convenience for creating listener objects.
   
7. * <P>
   
8. * Extend this class to create a <code>WindowEvent</code> listener
   
9. * and override the methods for the events of interest. (If you implement the
   
10. * <code>WindowListener</code> interface, you have to define all of
    
11. * the methods in it. This abstract class defines null methods for them
    
12. * all, so you can only have to define methods for events you care about.)
    
13. * <P>
    
14. * Create a listener object using the extended class and then register it with
    
15. * a Window using the window's <code>addWindowListener</code>
    
16. * method. When the window's status changes by virtue of being opened,
    
17. * closed, activated or deactivated, iconified or deiconified,
    
18. * the relevant method in the listener
    
19. * object is invoked, and the <code>WindowEvent</code> is passed to it.
    
20. *
    
21. * @see WindowEvent
    
22. * @see WindowListener
    
23. * @see <a >Tutorial: Writing a Window Listener</a>
    
24. *
    
25. * @author Carl Quinn
    
26. * @author Amy Fowler
    
27. * @author David Mendenhall
    
28. * @since 1.1
    
29. */
    
30. public abstract class WindowAdapter
    
31.     implements WindowListener, WindowStateListener, WindowFocusListener
    
32. {
    
33.     /**
    
34.      * Invoked when a window has been opened.
    
35.      */
    
36.     public void windowOpened(WindowEvent e) {}
    
37. 
    
38.     /**
    
39.      * Invoked when a window is in the process of being closed.
    
40.      * The close operation can be overridden at this point.
    
41.      */
    
42.     public void windowClosing(WindowEvent e) {}
    
43. 
    
44.     /**
    
45.      * Invoked when a window has been closed.
    
46.      */
    
47.     public void windowClosed(WindowEvent e) {}
    
48. 
    
49.     /**
    
50.      * Invoked when a window is iconified.
    
51.      */
    
52.     public void windowIconified(WindowEvent e) {}
    
53. 
    
54.     /**
    
55.      * Invoked when a window is de-iconified.
    
56.      */
    
57.     public void windowDeiconified(WindowEvent e) {}
    
58. 
    
59.     /**
    
60.      * Invoked when a window is activated.
    
61.      */
    
62.     public void windowActivated(WindowEvent e) {}
    
63. 
    
64.     /**
    
65.      * Invoked when a window is de-activated.
    
66.      */
    
67.     public void windowDeactivated(WindowEvent e) {}
    
68. 
    
69.     /**
    
70.      * Invoked when a window state is changed.
    
71.      * @since 1.4
    
72.      */
    
73.     public void windowStateChanged(WindowEvent e) {}
    
74. 
    
75.     /**
    
76.      * Invoked when the Window is set to be the focused Window, which means
    
77.      * that the Window, or one of its subcomponents, will receive keyboard
    
78.      * events.
    
79.      *
    
80.      * @since 1.4
    
81.      */
    
82.     public void windowGainedFocus(WindowEvent e) {}
    
83. 
    
84.     /**
    
85.      * Invoked when the Window is no longer the focused Window, which means
    
86.      * that keyboard events will no longer be delivered to the Window or any of
    
87.      * its subcomponents.
    
88.      *
    
89.      * @since 1.4
    
90.      */
    
91.     public void windowLostFocus(WindowEvent e) {}
    
92. }
    

复制代码

这种写是叫匿名内部类。格式：new <类或接口> <类的主体>
new WindowAdapter(){};
这句是的意思说：有一个类（匿名的），实现WindowAdapter这个抽象类，并返回一个这个类对象（不是WindowAdapter对象，抽象类不能new对象，只有实现它的类才能new对象）。

{}里面的内容是这个匿名类的主体，但看到这里空的，我也很纳闷！最起码的你应该把抽象类里的抽象方法都实现一下呀！
于是，把这句代码写到eclipse里面，Ctrl+单击==>打开源码，瞬间懂了，WindowAdapter下面有10个方法，但没有一个是抽象方法，所以这么写是可以的！
WindowAdapter wa=new WindowAdapter(){};这里还有传说中的多态 wa为父类引用