Data structure that supports O(1) append, prepend, first, last and size

FastPrependArrayList.java

import java.util.ArrayList;

public class FastPrependArrayList<A> {
    private ArrayList<A> appends = new ArrayList<A>();
    private ArrayList<A> prepends = new ArrayList<A>();

    public void append(A element) {
        appends.add(element);
    }

    public void prepend(A element) {
        prepends.add(element);
    }

    public A get(int index) {
        return index < prepends.size() ? prepends.get(prepends.size() - index - 1) : appends.get(index + prepends.size());
    }

    public int size() {
        return prepends.size() + appends.size();
    }

    public A first() {
        return get(0);
    }

    public A last() {
        return get(size() - 1);
    }
}

line 16: should be - @ : appends.get(index + prepends.size()); instead of + 👍