Question

My understanding of why arraylist is faster than a linkedlist is that with an arraylist you basically only need one action – update the reference at the end array element, whereas with a linked list you have to do much more e.g. create a new node, update 2 references, go through linked list and update the last node to point to the new one etc.

However I am not sure how java implement these. How does the arraylist know where the “last” element is, does it store a value of the last element or does it traverse the array and add a new element after the last?

And linked lists, do they store a reference to the last node in the list, or do they traverse the entire list to get to the end?

Answer 1

Look at the source:

ArrayList:

public boolean add(E e) {
    ensureCapacityInternal(size + 1);  // Increments modCount!!
    elementData[size++] = e;
    return true;
}      

LinkedList:

public boolean add(E e) {
    linkLast(e);
    return true;
}

void linkLast(E e) {
    final Node<E> l = last;
    final Node<E> newNode = new Node<>(l, e, null);
    last = newNode;
    if (l == null)
        first = newNode;
    else
        l.next = newNode;
    size++;
    modCount++;
}