首先说为什么要使用内部类：

1、实现多重继承

2、实现闭包（隐藏关键环节）

3、回调

常见内部类类型

1、非静态内部类

public class NoStaticInsideClass {
        private @Setter  String name;    
        private @Setter  int age;    
  
        class UserAction{        
              public void call() {            
                    System.out.println(name + " "+age);        
              }    
        }

        public static void main(String[] args) {        
            NoStaticInsideClass ni = new NoStaticInsideClass();        
            ni.setName("张三");        
            ni.setAge(18);        
            UserAction ua = ni.new UserAction();        
            ua.call();    
        }
}

​2、静态内部类

public class StaticInsideClass {    
         private static String name;    
         private static int age;    
         static class UserAction{        
              public void call() {            
                  System.out.println(StaticInsideClass.name + " "+StaticInsideClass.age);        
              }    
         }    

         public static void main(String[] args) {        
              StaticInsideClass.name = "张三";        
              StaticInsideClass.age = 18;        
              UserAction ua = new StaticInsideClass.UserAction();        
              ua.call();    
        }
}

​3、匿名内部类

public class AnonymousInsideClass {    
         private @Setter  String name;    
         private @Setter  int age;    
         UserAction ua = new  UserAction(){        
               public void call() {            
                     System.out.println(name + " "+age);        
               }    
         };    

         public static void main(String[] args) {        
               AnonymousInsideClass ni = new AnonymousInsideClass();        
               ni.setName("张三");        
               ni.setAge(18);        
               ni.ua.call();    
         }
}

实战

1、利用内部类实现多重继承

class Father {    
       public String name() {        
            return "张";    
       }
}

class Mather {    
       public String face() {        
            return "白色";    
       }
}

public class Child extends Father {    
        class Child2 extends Mather{        
             public String childPeculiarity(){            
                   return "继承了爸爸的姓（"+name() + "）和妈妈的皮肤（"+face()+")";        
             }    
        }    

        public static void main(String[] args) {        
             System.out.println("儿子的特点是：" + new Child().new Child2().childPeculiarity());    
        }
}

2、​利用内部类模拟按钮事件（Swing、RCP、Android等）

public interface BtnClickListener {    
        public void call();
}

public class Button {    
       public void addClickListener(BtnClickListener event) {        
             event.call();    
       }
}

public class UserClick {    
       /*** 匿名内部类     */    
       BtnClickListener bl = new BtnClickListener() {        
             @Override        
             public void call() {            
                   System.out.println("当用户点击了按钮后，执行了此方法");        
             }    
       };    

       public static void main(String[] args) {        
            new UserClick().triggerClick();    
       }    

      /*** 模拟触发按钮事件     */    
      public void triggerClick() {        
            new Button().addClickListener(bl);    
      }
}

​

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