Use of inner classes in Java-javaTutorial-php.cn

Use of inner classes in Java

黄舟

Release： 2017-01-18 15:45:12

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1. The role of inner classes

1. Inner classes provide better encapsulation. They can hide inner classes in outer classes and do not allow other classes in the same package to access them.

2. The methods of the inner class can directly access all data of the outer class.

3. More convenient to use.

2. Classification of inner classes:

1. Member inner class (as a member of the outer class)

2. Static inner class

3 .Method inner class (the inner class is inside a method of the outer class)

4.Anonymous inner class

3. The use of inner classes

1.Member inner class Usage:

<span style="font-family:Microsoft YaHei;font-size:18px;">package com.bluesky;  
  
public class Outer {  
      
    private int a =99;        //定义外部类的数据成员  
      
    public class Inner{      //该内部类作为外部类的一个成员  
          
        int b =88;            //内部类的数据成员  
          
        public void test(){  
            System.out.println("访问外部类的a："+a); //访问外部类的数据成员  
            System.out.println("访问内部类的b："+b); //访问内部列的数据成员  
        }  
    }  
  
    public static void main(String[] args) {  
          
        Outer o = new Outer();           //先生成一个外部类的对象实例  
           
        Inner in = o.new Inner();       //产生一个内部类的对象实例  
          
        in.test();                   //调用内部类的方法  
    }  
  
}</span>

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Use of inner classes in Java

2. Use of static inner classes

package com.bluesky;  
  
public class MethodOuter {  
      
    public void test(){  
          
        final int a=12;  
        int b=100;  
          
        class Inner{              //该内部类定义在外部类的方法的内部  
              
            public void print(){  
                int v=56;  
                System.out.println("访问外部类中的常量a："+a);  
                System.out.println("访问外部类中的b："+b);  
                System.out.println("访问内部类中的c："+v);  
            }  
        }  
          
        Inner in = new Inner();    //在方法体里面先产生内部类的对象实例  
        in.print();                //在外部类的方法里面调用内部类的方法  
          
    }  
  
    public static void main(String[] args) {  
          
        MethodOuter mo = new MethodOuter(); //产生外部类的对象实例  
          
        mo.test();                          //调用外部类的方法  
  
    }  
  
}

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Use of inner classes in Java

3. Use of static inner classes:

package com.bluesky;  
  
public class StaticOuter {  
      
    private static int a=99;  
    static int b =78;  
      
    public static class Inner{     //定义静态内部类  
        static int a=2;  
        public void test(){  
            System.out.println("访问外部类的b："+b);  
            System.out.println("访问外部类的a："+StaticOuter.a);  
            System.out.println("访问内部类的a："+a);  
        }  
    }  
  
    public static void main(String[] args) {  
          
        Inner in = new Inner();      //因为是静态的，所有可以直接产生对象实例  
        in.test();                   //调用静态内部类的方法  
  
    }  
  
}

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Use of inner classes in Java

Put anonymous inner classes at the back. Stay tuned!

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