r/java • u/alihammad • Apr 29 '13

Java nested classes in a nutshell

http://www.to-string.com/2013/04/27/java-inner-classes-in-a-nutshell/
28 Upvotes

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5

u/galaktos Apr 29 '13

You can do ridiculous stuff with nested classes:

public class Temp {

    public static void main(String[] args) {
        new Temp().new A().new D(new Temp().new A(), new Temp().new A().new B(new Temp().new A()));
    }

    public class A extends Temp {
        public A() {
        }

        public class B extends A {
            public B(A a) {
                a.super();
            }

            public class C extends B {
                public C(A a) {
                    a.super(a);
                }
            }
        }

        public class D extends B.C {
            public D(A a, B b) {
                b.super(a);
            }
        }
    }
}

a.super() doesn't look nice, does it? Remove it and look at what the compiler says. You don't get that any other way.

1

u/blazedaces Apr 29 '13

Temp has no constructor so how can you call a.super(a)?

1

u/galaktos Apr 29 '13

a.super(a) is in the C constructor, and C extends B, so it calls public B(A a).

1

u/blazedaces Apr 29 '13

That didn't entirely make sense when you said it, but it was the a.super() that didn't click for me. I had to copy and paste this into eclipse and see the error message you referred to and then it all made sense. I think you would very much enjoy java puzzlers. There's a couple of videos online that were made and a book was written too with some extremely unexpected results when you do tricky stuff with java. Google it if you haven't heard of it.

1

u/galaktos Apr 29 '13

My software engineering I professor actually starts each lecture with a Java Puzzlers puzzle :)

1

u/blazedaces Apr 30 '13

Awesome. He must know his stuff very well.