DequeList.java

import java.util.AbstractList;
import java.util.Deque;
import java.util.LinkedList;

public class DequeList<T> extends AbstractList<T> {
    private final Deque<T> deque;

    public DequeList(Deque<T> deque) {
        this.deque = deque;
    }

    @Override
    public T get(int index) {
        if (index < 0 || index >= size()) {
            throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size());
        }
        return deque.toArray(new Object[0])[index];
    }

    @Override
    public int size() {
        return deque.size();
    }

    @Override
    public boolean add(T element) {
        deque.addLast(element);
        return true;
    }

    @Override
    public void add(int index, T element) {
        if (index < 0 || index > size()) {
            throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size());
        }
        if (index == 0) {
            deque.addFirst(element);
        }
        else if (index == size()) {
            deque.addLast(element);
        } else {
            throw new UnsupportedOperationException("Insertion at index is not supported.");
        }
    }

    @Override
    public T remove(int index) {
        if (index < 0 || index >= size()) {
            throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size());
        }
        if (index == 0) {
            return deque.removeFirst();
        } else if (index == size() - 1) {
            return deque.removeLast();
        }
        throw new UnsupportedOperationException("Removal at index is not supported.");
    }
}