Question

In the university we were given the following code sample and we were being told, that there is a memory leak when running this code. The sample should demonstrate that this is a situation where the garbage collector can’t work.

As far as my object oriented programming goes, the only codeline able to create a memory leak would be

items=Arrays.copyOf(items,2 * size+1); 

The documentation says, that the elements are copied. Does that mean the reference is copied (and therefore another entry on the heap is created) or the object itself is being copied? As far as I know, Object and therefore Object[] are implemented as a reference type. So assigning a new value to ‘items’ would allow the garbage collector to find that the old ‘item’ is no longer referenced and can therefore be collected.

In my eyes, this the codesample does not produce a memory leak. Could somebody prove me wrong? =)

import java.util.Arrays;
public class Foo  
{  
private Object[] items;  
private int size=0;  
private static final int ISIZE=10;

public Foo()  
{  
  items= new Object[ISIZE];  
}  

public void push(final Object o){  
  checkSize();  
  items[size++]=o;  
}  

public Object pop(){  
  if (size==0)  
    throw new ///...  
  return items[--size];  
}  
private void checkSize(){  
  if (items.length==size){  
    items=Arrays.copyOf(items,2 * size+1);  
  }  
}  
}

Answer 1

Hint: the leak is in the pop method. Consider what happens to the references to a popped object …