Question

For example, is this code valid?.

class abc{
    int x,y;
    abc(int x,int y){
        this.x=x;
        this.y=y;
        while(true)
            update();
    }

    public void update(){
        x--;
        y--;
        if(y==0)
            this=null;
    }
 }

If the above is not valid, then please explain why. I am in need of a class that after certain iterations ceases to exist. Please suggest alternatives to the above approach.

Answer 1

No. The reason is that you do not make object null. When you say obj = null; You just put null to variable that previously hold reference to object. There are probably a lot of other references to the same object.

I think that what you want to do is to kind of invalidate object and make it garbage collected but take this decision inside the class. If this is the problem I’d recommend you to take a look on weak references.

Other possible solution is to implement kind of “smart reference” in java. You can create your class SmartReference that will hold the real reference to the object. The object should hold callback to this smart reference and call its method invalidate() that is something like your syntactically wrong expression this = null. You have to care not to refer to such objects directly but only via smart reference.

The only question is “why do you want to do this?”. Really, this will cause the code to be more complicated and unstable. Imagine: the object decides to invalidate itself, so the reference that “smart reference” is holding becomes null. Now all holders of this smart reference will get NPE when trying to use the object! This is exactly the reason the such mechanism does not exist in java and that application programmer cannot mange the memory directly.

Bottom line: remove all object references and let GC to do its hard job. Trust it. It knows to clean the garbage.