ch-assignment in kb ,need explanation of output:question 10

[Arjun Srivastava]

class Dozens{
int[] dz={1,2,3,4,5,6,7,8,9,10,11,12};
}
public class Eggs{
public static void main(String a[]){
Dozens [] da=new Dozens[3];
da[0]=new Dozens();
Dozens d=new Dozens();
da[1]=d;
d=null;
da[1]=null;
//do stuff
}
}

objects eliginle for garbage collection when line 12 is reached?
output:
five objects were created
and two objects are eligible for garbage collection.(second Dozens object and int array object)

please anyone explain me the answer how 5 objects are created here and why da[1] is eligible and why d is not?

[Prasad Kharkar]

here in this program we will go step by step
here is the code

  Dozens [] da=new Dozens[3];    

this create an array that is able to store 3 objects of type Dozens.
Remember that an array is always an object in java and here only one object is created and that is also of type Array
the three array elements can store objects of type Dozens but we have not created Dozen objects yet

  da[0]=new Dozens();   

This creates new Dozen object and now int[] dz is the instance member of class Dozens
so whenever we are creating Dozen object, in[] object is also getting created

  Dozens d=new Dozens();  

again same, two a dozen object is created which has instance member int[] object
hence 2 more objects are created and the total number becomes 5 objects



now look into the code for terse explanation

  class Dozens{
int[] dz={1,2,3,4,5,6,7,8,9,10,11,12};//every time a Dozen object is created, Array object is also created
}
public class Eggs{
public static void main(String a[]){
Dozens [] da=new Dozens[3];//object number one which is array type
da[0]=new Dozens();//two objects here , one is Dozen which has int[] object
Dozens d=new Dozens();//same as above hence total 5 objects
// here reference variable d refers to the Dozens object
da[1]=d;//also here da[1] refers to the same Dozens object referred by d 
d=null;// here we make d = null but da[1] also has reference to the object so it is not eligible for GC right now
da[1]=null; // here we make da[1] = null so the reference to the Dozen object is lost and also the in[] object in Dozen object is lost 
hence two objects are eligible for garbage collection
//do stuff
}
}
  

hope this helps
Happy to help
happy preparation

[Arjun Srivastava]

da[1]=null; // here we make da[1] = null so the reference to the Dozen object is lost and also the in[] object in Dozen object is lost
hence two objects are eligible for garbage collection

thanks for wonderfull explanation ,one more thing
hence two objects are eligible for garbage collection
1. int [] object
2. is d or da[1] (because da[1] is never a object it was a reference to d),please clear this thing also??

[Prasad Kharkar]

da[1] is not object and d is not an object also
even d is not the object
they both are the reference variables
and also
if there is some statement like

Dozens d = new Dozens();
da[1] = d

then do not assume that da[1] is referring to d
that means that
THIS IS CORRECT
da[1] is referring to the object that is referred by the reference variable d

IT IS NOT
da[1] is referring to d
above statement is completely wrong

[Arjun Srivastava]

thanks sir ,it really helps!!