Java member internal class instance analysis

1. Concept

refers to classes within classes, the outside ones are called external classes, and the inside ones are called internal classes.

2. Features

You can use all member variables and member methods(including private ones) in external classes

3. Common modifiers

(1) private

If our inner class does not want to be easily accessed by anyone , you can choose to use private to modify the inner class, so that we cannot access it through the method of creating an object. If you want to access it, you only need to define a public modified method in the outer class and call it indirectly. The advantage of this is that we can add some judgment statements to this public method to ensure data security.

class Outer {
      private class Inner {
          public void show() {
              System.out.println(“密码备份文件”);
          }
      }
      //使用getXxx()获取成员内部类，可以增加校验语句（文中省略）
      public Inner getInner() {
          return new Inner();
      }
      
      public static void main(String[] args) {
          Outer outer = new Outer();
          Outer.Inner inner = outer.getInner();
          inner.show();
      }
  }

(2)static

This kind of internal class modified by static is a member internal class according to its position, but it can also be called a static internal class , also often called nested inner classes. We will explain the specific content in detail below.

4. Example

Member internal class definition is inside a class.

public class Outer {
    public String outer ="outer";
    //定以外部类方法
    public void isOuter(){
        System.out.println(outer);
    }
    //定义内部类
    class Inner{
        public String inner ="inner";
        public void isInner(){
            System.out.println(inner);
        }
    }
}

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