Garbage Collection

[Sharmila Rishi]

Hi Ranchers,
Please consider the following code....

  class MyClass{}
 

 
class Test{
  private static void f(MyClass[] array){
array[0]=null;
array[1]=array[0];
array[2]=array[1];
array=null;
}
 
  public static void main(String[] args){
MyClass[] array=new MyClass[4];
for(int i=0;i<arra.length;i++)
  array[I]=new MyClass();
f(array);
System.gc();
}
}  

This is a question from WhizLabs.
Question:How many objects will be eligible for garbage collection before System.gc() is executed?

The given answer is 3.

I thought it was none since we only pass a reference of array object to the method f(array)and also since array variable in f() method is local to that method, it doesnt affect the array var in the main method.


Could anyone shed some light on it?

Thanks in advance.

-Sharmila Rishi.

[Keith Lynn]

The reference to the array itself is sent by value, but inside the method you can change the individual entries in the array using the formal parameter.

[Sharmila Rishi]

Thanks Keith.
So the statements

 array[0]=null;
array[1]=array[0];
        array[2]=array[1];  
 

are infact changing the values of the array....

while the statement

 array=null;   

is just setting the local variable to null.

Am I right..?


-Sharmila Rishi.
[ October 17, 2006: Message edited by: Sharmila Rishi ]

[Joe San]

Hi All,

Referring to the above code, how many objects are actually created? I guess that there are 8 objects created alltogether?

MyClass[] array=new MyClass[4]; //4 here and

for(int i=0;i<arra.length;i++)
array=new MyClass(); // 4 here since the for loop iterates 4 times.

Please anyone can tell on this?

Regards,
Jothi Shankar Kumar. S

[Keith Lynn]

Originally posted by Sharmila Rishi:
Thanks Keith.
So the statements

 array[0]=null;
array[1]=array[0];
        array[2]=array[1];  
 

are infact changing the values of the array....

while the statement

 array=null;   

is just setting the local variable to null.

Am I right..?


-Sharmila Rishi.

[ October 17, 2006: Message edited by: Sharmila Rishi ]

That's right.

[Keith Lynn]

Originally posted by Jothi Shankar Kumar Sankararaj:
Hi All,

Referring to the above code, how many objects are actually created? I guess that there are 8 objects created alltogether?

MyClass[] array=new MyClass[4]; //4 here and

for(int i=0;i<arra.length;i++)
array=new MyClass(); // 4 here since the for loop iterates 4 times.

Please anyone can tell on this?

Regards,
Jothi Shankar Kumar. S

In this line

MyClass[] array=new MyClass[4];

,

only one object is created, the array itself. Initially each reference in the array is null.

[Sharmila Rishi]

Thanks Keith.



-Sharmila Rishi.

[Bijendra S. Rajput]

for(int i=0;i<arra.length;i++)
array=new MyClass(); // error

When I am compiling this program, I am getting a error.

found : MyClass
required: MyClass[]
array = new MyClass();

and when I was compiling with MyClass[], then I am getting a error that array size is missing.

So, I am confused what will be the asnwer of this question.

Thanks,

Bijendra R.

[Keith Lynn]

Originally posted by Bijendra S. Rajput:
for(int i=0;i<arra.length;i++)
array=new MyClass(); // error

When I am compiling this program, I am getting a error.

found : MyClass
required: MyClass[]
array = new MyClass();

and when I was compiling with MyClass[], then I am getting a error that array size is missing.

So, I am confused what will be the asnwer of this question.

Thanks,

Bijendra R.

The original posted intended for the code to be

array[i] = new MyClass();

[Sharmila Rishi]

Sorry for the typo.

Also the for statement should be

 for(int i=0;i<array.length;i++)   

-Sharmila Rishi

[Bijendra S. Rajput]

Thanks Keith and Sharmila

Please give me a one more favour.

array = new MyClass();

// What we are doing in this line actually


Bijendra R.

[Ramu Malur S R]

Hi,

Considering the modified code, I think total 5 objects are created.

MyClass[] array=new MyClass[4]; //1 array object(with 4 references)

for(int i=0;i<array.length;i++)
array[i]=new MyClass(); // 4 MyClass objects.

Please correct me if I am wrong.

- Ramu

[Aniket Patil]

Right!