calling a function in a class's "owner" class

Question

Following pseudocode sums up my question pretty well I think...

class Owner {
    Bar b = new Bar();

    dostuff(){...}
}    

class Bar {
    Bar() {
        //I want to call Owner.dostuff() here
    }
}

Bar b is 'owned' (whats the proper word?) by Owner (it 'has a'). So how would an object of type Bar call Owner.dostuff()?

At first I was thinking super();, but that's for inherited classes. Then I was thinking pass an interface, am I on the right track?

@jason, suppose two classes have a field with the same reference to `b`? Which then would be the "owner"? — Kirk Woll, Feb 15 '12 at 20:04
@jason, right, but my point is that in such a scenario the concept of calling something on *the* "Owner" is nonsensical. — Kirk Woll, Feb 15 '12 at 20:06
@KirkWoll As other answers have noted, I'm more and more inclined to think that OP really wants an inner class. — Captain Giraffe, Feb 15 '12 at 20:15
I think the best way to name "Owner class" is to use the term "Enclosing class", but I've heard it called "container class" as well. — Yevgeniy Afanasyev, Mar 04 '15 at 22:50

Captain Giraffe · Accepted Answer · 2012-02-15T20:18:22.280

10

If dostuff is a regular method you need to pass Bar an instance.

class Owner {

   Bar b = new Bar(this);

   dostuff(){...}
}    

class Bar {
   Bar(Owner owner) {
      owner.dostuff();
   }
}

Note that there may be many owners to Bar and not any realistic way to find out who they are.

Edit: You might be looking for an Inner class: Sample and comments.

class Owner {

   InnerBar b = new InnerBar();

   void dostuff(){...}

   void doStuffToInnerBar(){
       b.doInnerBarStuf();
   }

   // InnerBar is like a member in Owner.
   class InnerBar { // not containing a method dostuff.
      InnerBar() { 
      // The creating owner object is very much like a 
      // an owner, or a wrapper around this object.
      }
      void doInnerBarStuff(){
         dostuff(); // method in Owner
      }
   }
}

edited Feb 15 '12 at 20:18

answered Feb 15 '12 at 20:04

Captain Giraffe

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@jason. If owner is an important concept for Bar, you might look in to the Inner class others have mentioned. This basically would make Bar a member in Owner. – Captain Giraffe Feb 15 '12 at 20:12
I dislike that this (like all answers so far) is tight coupling: `Bar` should not know about the `Owner` type except for that one function (declaration) it wants to talk to. Reusing `Bar` elsewhere gets complicated this way. Not sure how a simple "event property" aught to be done in JAVA though, it may need a bunch of Listeners code. – Barry Staes Aug 19 '15 at 09:50

score 3 · Answer 2 · edited Feb 15 '12 at 20:16

3

This would work:

class Owner {

    Bar b = new Bar(this);

    dostuff(){...}
}    

class Bar {
    Bar(Owner myOwner) {
        myOwner.dostuff();
    }
}

edited Feb 15 '12 at 20:16

Costique

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answered Feb 15 '12 at 20:06

Brian Driscoll

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score 3 · Answer 3 · edited May 23 '17 at 12:16

3

I think you are looking for nested Clases Nested Classes Sun

This way u can write outer.this.doStuff();

Have a look to that topic: Inner class call outer class method

edited May 23 '17 at 12:16

Community

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answered Feb 15 '12 at 20:06

Mario Corchero

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Ahh yes, this may work for my situation as well, thank you for reminding me of it. – jason Feb 15 '12 at 20:16

score 2 · Answer 4 · answered Feb 15 '12 at 20:04

2

In the way you're putting it, there is no way of calling the "owner" in Java.

Object A has a reference of object B doesn't mean that object B even knows that object A exists.

The only way to achieve this would be either though inheritance (like you said yourself), or by passing an instance of object Owner to the constructor of Bar.

answered Feb 15 '12 at 20:04

pcalcao

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"object B doesn't mean that object B even knows that object A exists" - Ive always thought this was odd. Some things work when theyre mutually aware, but I need to remember that this is not the default way it works. Was also secretly hoping for some mystical java-fu that I missed. – jason Feb 15 '12 at 20:10

score 2 · Answer 5 · answered Feb 15 '12 at 20:09

class Owner {
    Bar b = null;
    Owner(){
       b = new Bar(this);
    }
    dostuff(){...}
}    

class Bar {
    Owner o = null;
    Bar(Owner o) {
        this.o = o;
    }
}

Now, instance b of Bar has a reference to o of type Owner and can do o.doStuff() whenever needed.

score 1 · Answer 6 · answered Feb 15 '12 at 20:07

1

class Owner {

    Bar b = new Bar(this);

    dostuff(){...}
}    

class Bar {
    Bar(Owner owner) {
       owner.doStuff();
    }
}

answered Feb 15 '12 at 20:07

david a.

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score 1 · Answer 7 · answered Feb 15 '12 at 20:08

1

I think the way you have written the code, it is not possible to do. But if you declare Bar as inner class of Owner, you might get a closer solution.

answered Feb 15 '12 at 20:08

Bhushan

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score 1 · Answer 8 · answered Feb 15 '12 at 20:08

There are 3 possibilities :

1) making dostuff() static and call it like

Owner.dostuff()

2) Creating an instance of Owner inside the class Bar

class Bar {
   Owner o;
   public Owner() {
     o = new Owner();
     o.dostuff();
   }
}

3) Inject an Owner instance through the constructor

class Bar {
   public Owner(Owner o) {
     o.dostuff();
   }
}

calling a function in a class's "owner" class

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