内部类可以访问其所有实例成员，实例字段和其封闭类的实例方法。
参考如下实例 -

class Outer {
  private int value = 2017;
  public class Inner {
    public void printValue() {
      System.out.println("Inner: Value  = " + value);
    }
  } // Inner class ends here

  public void printValue() {
    System.out.println("Outer: Value  = " + value);
  }
  public void setValue(int newValue) {
    this.value = newValue;
  }
}

public class Main {
  public static void main(String[] args) {
    Outer out = new Outer();
    Outer.Inner in = out.new Inner();

    out.printValue();
    in.printValue();

    out.setValue(2018);

    out.printValue();
    in.printValue();
  }
}

上面的代码生成以下结果。

Outer: Value  = 2017
Inner: Value  = 2017
Outer: Value  = 2018
Inner: Value  = 2018

示例-1

以下代码显示如何访问内部类的内部变量。

public class Main {
  public static void main(String[] args) {
    Outer out = new Outer();
    Outer.Inner in = out.new Inner();

    out.printValue();
    in.printValue();

    out.setValue(3);

    out.printValue();
    in.printValue();
  }
}
class Outer {
  private int value = 1;
  public class Inner {
    private int value = 2;
    public void printValue() {
      System.out.println("Inner: Value  = " + value);
    }
  } // Inner class ends here
  public void printValue() {
    System.out.println("Outer: Value  = " + value);
  }
  public void setValue(int newValue) {
    this.value = newValue;
  }
}

上面的代码生成以下结果。

Outer: Value  = 1
Inner: Value  = 2
Outer: Value  = 3
Inner: Value  = 2

Inner类中的this关键字

以下代码显示如何在内部类中使用关键字 - this。

class Outer {
  private int value = 1;
  class QualifiedThis {
    private int value = 2;

    public void printValue() {
      System.out.println("value=" + value);
      System.out.println("this.value=" + this.value);
      System.out.println("QualifiedThis.this.value=" + QualifiedThis.this.value);
    }

    public void printHiddenValue() {
      int value = 2;
      System.out.println("value=" + value);
      System.out.println("this.value=" + this.value);

      System.out.println("QualifiedThis.this.value=" + QualifiedThis.this.value);
    }
  }
  public void printValue() {
    System.out.println("value=" + value);
    System.out.println("this.value=" + this.value);
  }  
}

public class Main {
  public static void main(String[] args) {
    Outer outer = new Outer();
    Outer.QualifiedThis qt = outer.new QualifiedThis();
    System.out.println("printValue():");
    qt.printValue();

    System.out.println("printHiddenValue():");
    qt.printHiddenValue();
    outer.printValue();
  }
}

上面的代码生成以下结果。

printValue():
value=2
this.value=2
QualifiedThis.this.value=2
printHiddenValue():
value=2
this.value=2
QualifiedThis.this.value=2
value=1
this.value=1

隐藏变量

如果实例变量名称被隐藏，必须使用关键字this或类名称以及关键字this限定其名称。

class TopLevelOuter {
  private int v1 = 100;

  // Here, only v1 is in scope
  public class InnerLevelOne {
    private int v2 = 200;

    // Here, only v1 and v2 are in scope
    public class InnerLevelTwo {
      private int v3 = 300;

      // Here, only v1, v2, and v3 are in scope
      public class InnerLevelThree {
        private int v4 = 400;

        // Here, all v1, v2, v3, and v4 are in scope

      }
    }
  }
}

从外部类

以下代码显示如何从外部类引用变量。

public class Test{
  private int value = 1;
  public class Inner {
    private int value = 2;

    public void printValue() {
      System.out.println("Inner: Value  = " + value);
      System.out.println("Outer: Value  = " + Test.this.value);
    }
  } // Inner class ends here

  public void printValue() {
    System.out.println("\nOuter - printValue()...");
    System.out.println("Outer: Value  = " + value);
  }

  public void setValue(int newValue) {
    System.out.println("\nSetting  Outer's value to " + newValue);
    this.value = newValue;
  }

}