Is Java's LinkedList optimized to do get(index) in reverse when necessary?

Question

I\'ve been working on some ways to optimize LinkedList\'s. Does anyone know if the Java default doubly-linked LinkedList class is optimized to do get() operatio

Answer 1

Yes it is. You can inspect the source code yourself: http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/LinkedList.java#LinkedList.entry%28int%29

LinkedList#get(int) is implemented as just

return entry(index).element;

where entry is a private method. entry's definition is:

private Entry<E> entry(int index) {
    if (index < 0 || index >= size)
        throw new IndexOutOfBoundsException("Index: "+index+
                                            ", Size: "+size);
    Entry<E> e = header;
    if (index < (size >> 1)) {
        for (int i = 0; i <= index; i++)
            e = e.next;
    } else {
        for (int i = size; i > index; i--)
            e = e.previous;
    }
    return e;
}

As you can see, it counts down from the end if index is greater than the midpoint of the list.