Java内部类总结
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原文链接：http://www.cnblogs.com/devinzhang/archive/2012/02/09/2344059.html
Java内部类其实在J2EE编程中使用较少，不过在窗口应用编程中特别常见，主要用来事件的处理。其实，做非GUI编程，内部类完全可以不用。
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内部类的声明、访问控制等于外部类有所不同，要灵活使用内部类来编写程序，还是有相当难度的，Java发明了这种难懂的玩意儿，在其他语言中是没有的，但是在Java中，内部类也相当的重要，尤其做GUI开发时候，事件的响应处理全靠内部类了。
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内部类所做的功能使用外部类也同样可以实现，只是有时候内部类做的更巧妙些。
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内部类按照其所在位置不同，可分为以下几种：
1、（普通的）内部类（最常见的内部类，内部类的定义与类成员平级，）2、方法内部类
3、匿名类
4、静态内部类
5、接口内部类 ? 一、内部类声明与访问 ? 1、内部类直接在类的内部进行声明。可以声明为private、protected、public或者默认访问权限，这个访问权限约定和外部类完全一样。 ? 2、内部类自动拥有对其外围类所有成员（方法、属性）的访问权。如果内部类和外部类成员的名字完全相同，在内部类方法中要访问外部类成员，则需要使用下面的方式来访问：外部类名.this.外部成员名，例如Outer.this.i++;? （看例子） ? 3、必须使用外部类对象来创建内部类对象，而不是直接去new一个。 格式为：外部对象名.new 内部类构造方法 ? 比如要创建一个内部类iner对象，需要这么做： ??????? Outer outer = new Outer();
??????? Outer.Inner iner = outer.new Inner(); ? /**?
* 内部类创建与初始化?
*?
* @author leizhimin 2009-7-17 13:51:52?
*/?
public?class?Outer {?
????????private?int?i = 10;?
????????private?int?y = 8;?
????????Outer() {?
????????????????System.out.println("调用Outer构造方法：outer");?
????????}?
????????public?void?sayMsg() {?
????????????????System.out.println("Outer?class!");?
????????}?
????????class?Inner {?
????????????????int?i = 1000;?
????????????????Inner() {?
????????????????????????System.out.println("调用Inner构造方法：inner");?
????????????????}?
????????????????void?innerMsg() {?
????????????????????????System.out.println(">>>>>Inner?class!");?
????????????????????????sayMsg();?
????????????????????????//访问内部类自己的成员i，也可以写成 this.i++?
????????????????????????this.i++;?
????????????????????????//访问外部类的成员 i和y?
????????????????????????Outer.this.i++;?
????????????????????????y--;?
????????????????}?
????????????????int?getI() {?
????????????????????????return?i;?
????????????????}?
????????}?
????????public?void?test() {?
????????????????Inner in =?new?Inner();?
????????????????in.innerMsg();?
????????}?
????????public?int?getI() {?
????????????????return?i;?
????????}?
????????public?void?setI(int?i) {?
????????????????this.i = i;?
????????}?
}?
class?Test1 {?
????????public?static?void?main(String[] args) {?
????????????????Outer outer =?new?Outer();?
????????????????outer.test();?
????????????????System.out.println(outer.getI());?
????????????????System.out.println("-------1--------");?
????????????????Outer.Inner iner = outer.new?Inner();?
????????????????iner.innerMsg();?
????????????????System.out.println(iner.getI());?
????????????????System.out.println("-------2--------");?
????????????????System.out.println(outer.getI());?
????????}?
} ? 运行结果： 调用Outer构造方法：outer?
调用Inner构造方法：inner?
>>>>>Inner?class!?
Outer?class!?
11?
-------1--------?
调用Inner构造方法：inner?
>>>>>Inner?class!?
Outer?class!?
1001?
-------2--------?
12?
Process finished with exit code 0 ? 二、内部类与接口 ? 1、内部类可以实现接口。 2、内部类之间相互可见，但并非内部类之间方法都可见。 ? public?interface?Foo{?
?????????void?say();?
} ? public?interface?Bar {?
????????void?readme();?
} ? /**?
* 内部类实现接口?
*?
* @author leizhimin 2009-7-17 14:57:50?
*/?
public?class?Test2 {?
????????public?static?void?main(String[] args) {?
????????????????Outer outer =?new?Outer();?
????????????????Foo f = outer.genFoo();?
????????????????Bar b = outer.genBar();?
????????????????f.say();?
????????????????b.readme();?
????????}?
}?
class?Outer {?
????????private?class?FooImpl?implements?Foo {?
????????????????public?void?say() {?
????????????????????????System.out.println("say foo!");?
????????????????}?
????????}?
????????private?class?BarImpl?implements?Bar {?
????????????????public?void?readme() {?
????????????????????????System.out.println("say bar!");?
????????????????}?
????????}?
????????public?Foo genFoo() {?
????????????????return?new?FooImpl();?
????????}?
????????public?Bar genBar() {?
????????????????return?new?BarImpl();?
????????}?
} ? 输入结果： say foo!?
say bar!?
Process finished with exit code 0 ? 三、访问权限 ? 外部类分两种：
一种嵌入了内部类声明代码外部类，称为直接外部类。
另一种是与内部类没有任何关系的外部类，称为外部类。 ? 在同一个直接外部类中，内部类之间所有的方法都是相互可见的，包含在直接外部类的main()中可见。
在外部类中，要看到一个类的内部类成员，则至少要求这个内部类的class和成员权限大于或等于protected。 ? /**?
* 内部类实现接口?
*?
* @author leizhimin 2009-7-17 14:57:50?
*/?
public?class?Test2 {?
????????public?static?void?main(String[] args) {?
????????????????Outer o =?new?Outer();?
????????????????Outer.Bar b = o.genBar();?
????????????????b.readme();?
????????}?
}?
class?Outer {?
????????protected?class?Foo {?
????????????????protected?void?say() {?
????????????????????????System.out.println("say foo!");?
????????????????}?
????????????????private?void?test() {?
????????????????????????System.out.println("----test------");?
????????????????}?
????????}?
????????protected?class?Bar {?
????????????????protected?void?readme() {?
????????????????????????System.out.println("say bar!");?
????????????????????????new?Foo().test();?
????????????????}?
????????}?
????????public?Foo genFoo() {?
????????????????return?new?Foo();?
????????}?
????????public?Bar genBar() {?
????????????????return?new?Bar();?
????????}?
} ? 四、方法内部类 ? 方法内部类只在该方法内部可见，方法内部类可以定义在方法中的任何位置。 /**?
* 内部类实现接口?
*?
* @author leizhimin 2009-7-17 14:57:50?
*/?
public?class?Test2 {?
????????public?static?void?main(String[] args) {?
????????????????Outer outer =?new?Outer();?
????????????????Foo f = outer.genFoo();?
????????????????Bar b = outer.genBar();?
????????????????f.say();?
????????????????b.readme();?
????????}?
}?
class?Outer {?
????????public?Foo genFoo() {?
????????????????//方法内的内部类?
????????????????class?FooImpl?implements?Foo {?
????????????????????????public?void?say() {?
????????????????????????????????System.out.println("say foo!");?
????????????????????????}?
????????????????}?
????????????????return?new?FooImpl();?
????????}?
????????public?Bar genBar() {?
????????????????Bar b =?null;?
????????????????if?(true) {?
????????????????????????//任意位置的内部类?
????????????????????????class?BarImpl?implements?Bar {?
????????????????????????????????public?void?readme() {?
????????????????????????????????????????System.out.println("say bar!");?
????????????????????????????????}?
????????????????????????}?
????????????????????????b =?new?BarImpl();?
????????????????}?
????????????????return?b;?
????????}?
} ? 运行结果： say foo!?
say bar!?
Process finished with exit code 0 ? 五、匿名类 ? 匿名类不给出类名，直接定义一个类，通常这个类实现了某种接口或者抽象。匿名类的访问权限更没有讨论价值了，看个例子就行了。 ? 在一些多线程程序中比较常见，有点变态，呵呵。 /**?
* 匿名类.?
*?
* @author leizhimin 2009-7-17 15:56:17?
*/?
public?class?Test3 {?
????????public?Foo f =?new?Foo() {?
????????????????public?void?say() {?
????????????????????????System.out.println("O(∩_∩)O哈哈~!");?
????????????????}?
????????};?
????????public?Foo test() {?
????????????????return?new?Foo() {?
????????????????????????public?void?say() {?
????????????????????????????????System.out.println("say foo!");?
????????????????????????}?
????????????????};?
????????}?
????????public?static?void?main(String[] args) {?
????????????????Test3 t =?new?Test3();?
????????????????t.f.say();?
????????????????t.test().say();?
????????}?
}?
interface?Foo {?
????????void?say();?
} ? 运行结果： O(∩_∩)O哈哈~!?
say foo!?
Process finished with exit code 0 ? /**?
* 普通类的匿名初始化?
*?
* @author leizhimin 2009-7-17 16:13:31?
*/?
public?class?Fk {?
????????private?String x;?
????????public?Fk(String x) {?
????????????????this.x = x;?
????????}?
????????@Override?
????????public?String toString() {?
????????????????return?"Fk{"?+?
????????????????????????????????"x='"?+ x + '\'' +?
????????????????????????????????'}';?
????????}?
}?
class?Test4 {?
????????public?Fk hehe() {?
????????????????//把后面的一对大括号去掉呢，呵呵?
????????????????return?new?Fk("fk") {?
????????????????};?
????????}?
????????public?static?void?main(String[] args) {?
????????????????Test4 t =?new?Test4();?
????????????????Fk f = t.hehe();?
????????????????System.out.println(f);?
????????}?
} ? 运行结果： Fk{x='fk'}?
Process finished with exit code 0 ? 还有一个不得不提的经典实例，来自thining in java，有改动： interface?Service {?
????void?method1();?
????void?method2();?
}?
interface?ServiceFactory {?
????Service getService();?
}?
class?Implementation1?implements?Service {?
????private?Implementation1() {}?
????public?void?method1() {System.out.println("Implementation1 method1");}?
????public?void?method2() {System.out.println("Implementation1 method2");}?
????public?static?ServiceFactory factory =?new?ServiceFactory() {?
????????????public?Service getService() {?
????????????????return?new?Implementation1();?
????????????}?
????????};?
}?
class?Implementation2?implements?Service {?
????private?Implementation2() {}?
????public?void?method1() {System.out.println("Implementation2 method1");}?
????public?void?method2() {System.out.println("Implementation2 method2");}?
????public?static?ServiceFactory factory =?new?ServiceFactory() {?
????????????public?Service getService() {?
????????????????return?new?Implementation2();?
????????????}?
????????};?
}?
public?class?Factories {?
????public?static?void?serviceConsumer(ServiceFactory fact) {?
????????Service s = fact.getService();?
????????s.method1();?
????????s.method2();?
????}?
????public?static?void?main(String[] args) {?
????????serviceConsumer(Implementation1.factory);?
????????serviceConsumer(Implementation2.factory);?
????}?
} ? 这个应用给了我们很多思考，我就不说了，不同人看了会有不同的感受。 ? 内部类的巧妙使用会让你的代码很牛，如果要形容下，那就是：没看懂的时候感觉神出鬼没，看懂后感觉鬼斧神工。不过这些代码多了，别人想看懂都难，想看懂你思路就难上加难了。呵呵！ ? 六、静态内部类 ? 静态内部类是static class型的内部类，这种内部类特点是：它不能访问外部类的非静态成员。要创建静态内部类对象时候，也不需要外部类对象了，直接可以： new 外部类名.内部类构造方法 来创建，给个例子： /**?
* 静态内部类?
*?
* @author leizhimin 2009-7-17 16:53:05?
*/?
public?class?Outer {?
????????public?static?int?i =500;?
????????protected?static?class?Inner {?
????????????????int?i =100;?
????????????????String name;?
????????????????Inner(String name) {?
????????????????????????this.name = name;?
????????????????}?
????????????????void?sayHello() {?
????????????????????????System.out.println("Hello "?+ name);?
????????????????????????Outer.i++;?
????????????????}?
????????}?
????????public?Inner genInner(String name) {?
????????????????return?new?Inner(name);?
????????}?
}?
class?Test {?
????????public?static?void?main(String[] args) {?
????????????????Outer.Inner in1 =?new?Outer.Inner("1111");?
????????????????in1.sayHello();?
????????????????System.out.println(Outer.i);?
????????????????Outer.Inner in2 =?new?Outer().genInner("2222");?
????????????????in2.sayHello();?
????????????????System.out.println(Outer.i);?
????????}?
} ? 运行结果： Hello 1111?
501?
Hello 2222?
502?
Process finished with exit code 0 ? 七、接口内部类 ? 接口内部类自动都是public static的，相当于为接口定义了一种变量类型，这在java的设计中就有使用，比如在HashMap中，就有： static class Entry<K,V> implements Map.Entry<K,V> ? 下面我给个例子， /**?
* 接口内部类?
*?
* @author leizhimin 2009-7-17 17:20:28?
*/?
public?interface?AInterface {?
????????void?readme();?
????????class?Inner1?implements?AInterface {?
????????????????public?void?readme() {?
????????????????????????System.out.println("我是一个接口内部类");?
????????????????}?
????????}?
}?
class?Main {?
????????public?static?void?main(String[] args) {?
????????????????AInterface.Inner1 in1 =?new?AInterface.Inner1();?
????????????????in1.readme();?
????????}?
} ? 八、内部的类的嵌套 ? 所谓内部类嵌套，就是内部类里面再定义内部类。其实这种用法还真没见过，试试写个简单例子看看吧： ? /**?
* 嵌套内部类?
*?
* @author leizhimin 2009-7-17 17:33:48?
*/?
public?class?Outer {?
????????private?void?f0() {?
????????????????System.out.println("f0");?
????????}?
????????class?A {?
????????????????private?void?a() {?
????????????????????????f0();?
????????????????????????System.out.println("a");?
????????????????}?
????????????????class?B {?
????????????????????????protected?void?b() {?
????????????????????????????????a();?
????????????????????????????????System.out.println("b");?
????????????????????????}?
????????????????}?
????????}?
}?
class?Test{?
????????public?static?void?main(String[] args) {?
????????????????Outer o =?new?Outer();?
????????????????Outer.A????a =???? o.new?A();?
????????????????Outer.A.B b = a.new?B();?
????????????????b.b();?
????????}?
} ? 运行结果： f0?
a?
b?
Process finished with exit code 0 ? 八、内部类的继承 ? 内部类的继承，可以继承内部类，也可以继承外部类。 /**?
* 内部类的继承，可以继承内部类，也可以继承外部类?
*?
* @author leizhimin 2009-7-22 13:50:01?
*/?
public?class?Outer {?
????????class?Inner {?
????????????????void?doSomething() {?
????????????????????????System.out.println("Inner doing ...");?
????????????????}?
????????}?
????????class?Inner2?extends?Inner {?
????????????????void?doSomething() {?
????????????????????????System.out.println("Inner2 doing ...");?
????????????????}?
????????????????void?readme() {?
????????????????????????System.out.println("HeHe!");?
????????????????}?
????????}?
}?
class?Test {?
????????public?static?void?main(String[] args) {?
????????????????Outer outer =?new?Outer();?
????????????????Outer.Inner in = outer.new?Inner();?
????????????????Outer.Inner2 in2 = outer.new?Inner2();?
????????????????in.doSomething();?
????????????????in2.doSomething();?
????????????????in2.readme();?
????????}?
} ? 运行结果： Inner doing ...?
Inner2 doing ...?
HeHe!?
Process finished with exit code 0 ? ? 总结： ? 内部类是Java中最复杂深奥的概念之一，而且内部类在访问控制，修饰符，继承，实现，抽象，序列化等等很多方面都是一个很让人迷惑的问题，在实际中，这些问题也许永远没机会没时间搞清，但是一般说来，懂得以上的内部类的知识就足够用了。 ?
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请参见：http://lavasoft.blog.51cto.com/62575/179484/转载于:https://www.cnblogs.com/devinzhang/archive/2012/02/09/2344059.html
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