Objects - GC

[Lovleen Gupta]

The question is - how many objects are eligible for garbage collection at //doStuff?

class Cardboard{
    Short story = 5;
    Cardboard go(Cardboard cb){
        cb = null;
        return cb;
    }
    
    public static void main(String[] args){
        Cardboard c1 = new Cardboard();
        Cardboard c2 = new Cardboard();
        Cardboard c3 = c1.go(c2);
        c1= null;
        //doStuff
    }
}

My understanding says that there should be 4 objects (c1, c1.story, c2, c2.story). But the answer is 2. Please explain why is it so?

Thanks.

[Chandra Bhatt]

    
class Cardboard{
    Short story = 5;
    Cardboard go(Cardboard cb){
        cb = null;
        return cb;
    }
    
    public static void main(String[] args){
        Cardboard c1 = new Cardboard();
        Cardboard c2 = new Cardboard();
        Cardboard c3 = c1.go(c2);
        c1= null;
        //doStuff
    }
}
 

My understanding says that there should be 4 objects (c1, c1.story, c2, c2.story). But the answer is 2. Please explain why is it so?

Hi Guptajee,
You should always see at how many times "new" is being used at first hand.
Inside the main method you created 2 objects; dont forget Short story =5; in the class definition, it is for every object, Short is wrapper not primitive. Inside the go method there wont be affect of making bs =null to the original main reference. It would have local impact at you know copy of the reference is passed to the method so if any internal modification is made to the object as "changing Person's name or age" using passed reference, it would affect the calling method but setting the reference to null in the called method wont affect the calling method object reference; so dont worry about that.

When you set the c1= null; Two objects become eleigible for garbage collection; the first the object referenced by c1 and the object referenced by the story referecen that is encapsulated in the object. So two objects would be eligible for garbage collection.


Hope this helps,

Thanks and Regards,
cmbhatt

[Rajeswari Kumar]

Hi Lovleen
This issue is already discussed. Please check the link
https://coderanch.com/t/262041/java-programmer-SCJP/certification/Garbage-Collection-any-one-explain

regards
Rajeswari

[Lovleen Gupta]

Thanks Chandra & Rajeswari..
It is clear now..!