Quiz on anonymous classes

[Marlene Miller]

Here is a quiz based on K&B Chapter 8, Self Test 12, page 485-486
This is a lean version of the example.

class A {
    class B {}
//
    public static void main(String[] args) {
        A x = new A() {};
        A.B y = x.new B() {};  //really difficult!
    }
}

Quiz: Replace the anonymous class declarations with named class declarations and instantiate the classes. Try to preserve the class structures and relationships.
For example,
class C extends A {}
A x = new C();
[ August 14, 2003: Message edited by: Marlene Miller ]

[Marlene Miller]

Hint:
Here is an analysis of the class structures and relationships.

A$B.class        member class of A
A$1.class        anonymous inner class of A
A$2.class        anonymous inner class of A
A.class
//
class A$1 extends A {
    A$1();
}
class A$2 extends A. B {
    A$2(A);
}
class A. B extends java.lang.Object
{
    private final A this$0;    //synthetic reference to enclosing instance of A
    A.B(A);
}

[ August 14, 2003: Message edited by: Marlene Miller ]

[Marlene Miller]

Answer: Part I.

class A {
    class B {}
//
    static void main(String[] args) {
        class C extends A {}
        class D extends A.B {
            D(A ref) { ref.super(); }
        }
//
        C c = new C();
        A a = c;
//
        D d = new D(a);
        A.B b = d;
    }
}

In the first example, the anonymous subclass of A.B is an inner class of A. The reference to the enclosing instance is passed upstairs through the constructor of the anonymous class. The subclass is instantiated in a static context. It does not need the reference itself. That is difficult for me to understand.
[ August 14, 2003: Message edited by: Marlene Miller ]

[Marlene Miller]

Answer: Part II.
The new classes have the same structure as the old classes.

A$B.class
A$1$C.class
A$1$D.class
A.class
//
class A$1$C extends A {
    A$1$C();
}
class A$1$D extends A. B {
    A$1$D(A);
}
class A. B extends java.lang.Object
{
    private final A this$0;
    A.B(A);
}

My way of viewing the heap.

 -----         -----
|  A  | <---- |a B  |
|- - -|       |- - -|
|  C  |       |  D  |
 -----         -----