CODEWITHSUNDEEP
javaconstructorinner-classes
Don Li
Don Li

Reputation: 1095

How to initialize a class inheriting from an inner class?

How to initialize a class inheriting from an inner class? Why foo1.this() won't compile?

class Foo1 {
    class Inner {
    }
}

class Foo2 extends Foo1.Inner {
    //Foo2(Foo1 foo1) {foo1.this();} //won't compile
    Foo2(Foo1 foo1) {foo1.super();}
}

Upvotes: 0

Views: 232

Answers (3)

henko
henko

Reputation: 763

I'm not sure I understand what foo1.this(); is supposed to do. Perhaps you are trying to call the default constructor of Inner. Since Inner is a not a static class, it does not have a no argument constructor. It only looks that way. In reality, it has a constructor which takes a Foo1 argument containing the reference to its parent object.

The call to foo1.super(), however, will work just fine. It will call the constructor of the new Inner instance with foo1 as implicit parent reference. That is, the new Inner instance will be tied to the given Foo1 instance.

As others have pointed out, you can of cause make your Inner class static, in which case it does not contain an implicit reference to a Foo1 instance. Then you can simply call super(); in your Foo2 constructor.

Upvotes: 1

Mattias Isegran Bergander
Mattias Isegran Bergander

Reputation: 11909

If you declare the Inner class static you can do it else you need an instance of the outer class Foo1.

class Foo1 {
    static class Inner {
    }
}

But your direct questions seems strange:

foo1.this(); //won't compile

What are you trying to do here? Call a method called "this" it looks like, but hoping to use the no-argument constructor perhaps? Just use this() if so.

Upvotes: 2

nsfyn55
nsfyn55

Reputation: 15363

Make your inner class static. There is no instance from which to get a non static class definition

Upvotes: 0

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