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abstract类是不能创建实例的，可为什么会出现。。。。？

创建：2005-10-28 00:08:14
作者：Unlinux
来自: http://www.Unlinux.com

问：
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我在J2SDK1。4。2的文档中看到这样的类
public abstract class MouseAdapter extends Object implements MouseListener

public abstract class WindowAdapter extends Object
implements WindowListener, WindowStateListener, WindowFocusListener

既然抽象类不能创建实例，那为什么new WindowAdapter(...){.....}

能被编译通过呢？

而且事件被执行得很好。

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答：
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Did you notice the difference between:

1, new WindowAdapter(..)
2, new WindowAdapter(..) {...}

The first tries to create an instance of WindowAdapter, we kmow it will fail, because WindowAdapter is an abstract class.

The second is doing a different thing. It creates a new anonymous class which extends WindowAdapter and the implementation is in the {...}

If you do not implement all abstract methods in the WindowAdapter, you still receive a compiler error.

Java supports anonymous class for programmers convenience. In this case, you do not have to write a small class in its own .java file and you do not care its name.

Anonymous class also support interfaces with the same syntax:

You have:

abstract class ClassA
interface InterfaceA

Then you can write code like:

new ClassA() { implementation }
new InterfaceA() { implementation }

In a compiler's eye, they are exactly the same as:

class Class$1 extends ClassA {implementation}
new Class$1(..)

class Class$2 implements InterfaceA {implementation}
new Class$2(..)

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转载自：http://www.unlinux.com/doc/java/20051028/5500.html

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abstract类是不能创建实例的，可为什么会出现。。。。？