Which is more efficient? Using the same arraylist by using removeAll() or creating the new arraylist

Question

Im using arraylist to compare the elements in my selenium webdriver script in which I have compare the elemets from two different pages.

So which one is more efficient ?

Using same arraylist or creating the new one?

Most of the times I would create a new Arraylist and let the garbage collector decompose the list items references in its own sweet time. — Mritunjay, Sep 26 '17 at 07:05

score 0 · Answer 1 · answered Sep 26 '17 at 07:09

The source code for removeAll()(As defined in AbstractCollection):

public boolean removeAll(Collection<?> c) {
    Objects.requireNonNull(c);
    boolean modified = false;
    Iterator<?> it = iterator();
    while (it.hasNext()) {
        if (c.contains(it.next())) {
            it.remove();
            modified = true;
        }
    }
    return modified;
}

The source code for clear()(As defined in ArrayList):

public void clear() {
    modCount++;

    // clear to let GC do its work
    for (int i = 0; i < size; i++)
        elementData[i] = null;

    size = 0;
}

clear() is much faster since it doesn't have to deal with all those extra method calls, but I think that instantiate a new ArrayList is the most efficient, in particular in a very big ArrayList (no need to iterate over the collection).

Which is more efficient? Using the same arraylist by using removeAll() or creating the new arraylist

1 Answers1