Question about GC and Objects

[Christian Joseph]

i stumbled about this Test in SCJP by Kat and bertes . ..

on page 274

public class Dozens {
	int[] dz = {1,2,3,4,5}; //one int array object
}
class Eggs{
	public static void main(String[] args){
		
		Dozens[] da = new Dozens[3]; //two array object
		da[0] = new Dozens(); //third object
		Dozens d = new Dozens(); //fourth object not connected to array "da"
		da[1] = d; // <== is this a new "d" ( i mean a copy? )     
		// i think its the fifth one
		
		d = null; //one gc
		da[1] = null; //two gc
	}
}

Which two are true about the objects created within main(), and eligible for garbage collection when line 14 is reached?

the answer is FIVE objects are created and two object are eligible for GC...

can someone help me
explain please

[Naveen Madarapu]

public class Dozens {  
    int[] dz = {1,2,3,4,5}; 
}  
class Eggs{  
    public static void main(String[] args){  
          
        Dozens[] da = new Dozens[3]; //here create one array object type Dozens
        da[0] = new Dozens(); //here two objects are created one is new Dozens() and one is containing instance variable int[] dz array 
        Dozens d = new Dozens(); //here also same two objects are created one is new Dozens() and it's containing int[] dz array  
        da[1] = d;   // you are copying reference  
                 
        d = null; da[1] = null; //here both are pointing to d reference object so d reference no more it means d object and it's containing int[] dz objects are eligible for GC
    }  
}  

if you face this kind of question you need to draw diagram to know which reference is point to which object. which one is eligible to GC.

[Christian Joseph]

i get it now, Thanks! Ms. Naveen Madarapu...

so whenever i say "new Dozens" it will crreate a Dozen Object, PLUS a instance member like the int in the example

then since "d" reference object "NEW DOZENS()" has pointing two f***n thing the "d" and the "d[1]", which is become null, the line broke and then the DOzen of d and the int object, where left on the blackhole

thanks ! did i get it?

[Ogeh Ikem]

The statement Dozens[] da = new Dozens[3] creates the first object i.e. a Dozens array (1). The statement da[0] = new Dozens() creates 2 objects i.e. a Dozens object (2) and an int array (3). The statement Dozens d = new Dozens() creates 2 objects i.e. a Dozens object (4) and an int array (5). Total objects created is 5.

The statements d = null and da[1] = null make objects (4) and (5) eligible for GC at line 14. Both statements are necessary or else objects (4) and (5) wont be eligible for GC at line 14.

public class Dozens {
	int[] dz = {1,2,3,4,5}; //one int array object
}
class Eggs{
	public static void main(String[] args){
		
		Dozens[] da = new Dozens[3]; //two array object
		da[0] = new Dozens(); //third object
		Dozens d = new Dozens(); //fourth object not connected to array "da"
		da[1] = d; // <== is this a new "d" ( i mean a copy? )     
		// i think its the fifth one
		d = null; //one gc
		da[1] = null; //two gc
        // do stuff
	}
}

[Christian Joseph]

Ogeh Ikem wrote:The statement Dozens[] da = new Dozens[3] creates the first object i.e. a Dozens array (1). The statement da[0] = new Dozens() creates 2 objects i.e. a Dozens object (2) and an int array (3). The statement Dozens d = new Dozens() creates 2 objects i.e. a Dozens object (4) and an int array (5). Total objects created is 5.

The statements d = null and da[1] = null make objects (4) and (5) eligible for GC at line 14. Both statements are necessary or else objects (4) and (5) wont be eligible for GC at line 14.

THANKS!!! IT REALLY help me alot hearing from you guys!!