Best way to reset the value in List

[Raymond Tong]

Hi,

I have got a List with approximate 60k elements
and a Set with approximate 40k elements.

I need to reset the List to point to the elements inside the Set.
I found 2 approachs and have done some benchmark test but could not give me much information.

1) List.clear();
List.addAll(Set);

2) List = Arrays.asList(Set.toArray());

Which one would have better performance or there would have a better alternative?
(The size of List and Set may varies)

Raymond

[Madhan Sundararajan Devaki]

I believe, in option 1, you are re-using the List object, whereas in option 2, you are destroying existing List object and then creating a new one.

I guess, option 1 is preferable.

[William Brogden]

The clear operation on an existing list does this:

    /**
     * Removes all of the elements from this list.  The list will
     * be empty after this call returns.
     */
    public void clear() {
	modCount++;

	// Let gc do its work
	for (int i = 0; i < size; i++)
	    elementData[i] = null;

	size = 0;
    }

(java.util.ArrayList source)
operating on every single element! Therefore it will be slow slow slow compared to creating a new empty list.

Furthermore, if you can create the new list with the required size, as option 2 does, you avoid the expansion overhead.

Bill