java如何从内部内部类实现对封闭类的访问？

Question

I have created an inner class in an inner class :

public class EnclosingClass {

    public class InnerClass {
        private EnclosingClass getEnclosing() {
            return EnclosingClass.this;
        }

        public class InnerInnerClass {
            private InnerClass getEnclosing() {
                return InnerClass.this;
            }

            private EnclosingClass getEnclosingOfEnclosing() {
                return EnclosingClass.this;
            }
        }        
    }
}

I have been surprised that java allows the InnerInnerClass to access directly the EnclosingClass . How is this code implemented internally by Java?

The InnerInnerClass keeps two pointers (one on the InnerClass and the other on the EnclosingClass ) or the InnerInnerClass access the EnclosingClass through the InnerClass ?

Answer 1

You just need to disassemble the resulting class with javap to see what's going on:

private EnclosingClass getEnclosingOfEnclosing();
  Code:
     0: aload_0
     1: getfield      #1                  // Field this$1:LEnclosingClass$InnerClass;
     4: getfield      #3                  // Field EnclosingClass$InnerClass.this$0:LEnclosingClass;
     7: areturn

So first it gets the instance of the directly enclosing class, then it gets the "top-level" enclosing class from that.

Answer 2

如果内部类不是“静态”，则它们在包含它们的类的内部包含引用。

Answer 3

除非你使内部类是静态的，否则它确实引用了它所存在的实例，并且可以引用它的成员（包括private），内部内部类，内部内部内部类等也是如此。

Answer 4

public and private is a pointer issue, it's a compiler issue.

The question is one of the compiler enforcing the scope of a class/variable/method. Because the private method getEnclosing() falls with the the scope of InnerClass , it can be accessed throughout that class.

Note that pointers have nothing to do with the issue.
Using reflection you can still access private members of a class.