Please do the TODO this is some basis about array import java.lang.reflect.Array; import java.util.Arrays; import java.util.Optional; class NoSuchElementE extends Exception {} public abstract class DequeueArray { protected Optional[] elements; protected int capacity, front, back, size; // // data stored in locations: // front+1, front+2, ... back-2, back-1 (all mod capacity) // // common cases: // front points to an empty location // back points to an empty location // adding to front decreases 'front' by 1 // adding to back increases 'back' by 1 // removing does the opposite // // |-------------------------| // | 4 5 6 _ _ _ _ _ _ 1 2 3 | // |-------------------------| // /\ /\ /\ // back front capacity // @SuppressWarnings("unchecked") DequeueArray(int initialCapacity) { elements = (Optional[]) Array.newInstance(Optional.class, initialCapacity); Arrays.fill(elements, Optional.empty()); capacity = initialCapacity; front = capacity - 1; back = 0; size = 0; } @SuppressWarnings("unchecked") public void clear() { elements = (Optional[]) Array.newInstance(Optional.class, 1); Arrays.fill(elements, Optional.empty()); capacity = 1; front = 0; back = 0; size = 0; } public int size () { return size; } // --- real work begins --- // /** * Adds the given elem to the front of the dequeue * If there is no room, grow the dequeue first */ public void addFirst(E elem) { // TODO } /** * Adds the given elem to the back of the dequeue * If there is no room, grow the dequeue first */ public void addLast(E elem) { // TODO } public E getFirst() throws NoSuchElementE { return elements[Math.floorMod(front+1,capacity)].orElseThrow(NoSuchElementE::new); } public E getLast() throws NoSuchElementE { return null; // TODO } /** * Removes (and returns) the first element in the dequeue * If the dequeue is empty, throw an exception instead */ public E removeFirst() throws NoSuchElementE { return null; // TODO } /** * Removes (and returns) the last element in the dequeue * If the dequeue is empty, throw an exception instead */ public E removeLast() throws NoSuchElementE { return null; // TODO } // the following methods are for debugging and testing Optional[] getElements () { return elements; } int getCapacity () { return capacity; } int getFront () { return front; } int getBack () { return back; } abstract void grow (); } // --------------------------------------------------------- class DequeueArrayDouble extends DequeueArray { DequeueArrayDouble (int initialCapacity) { super(initialCapacity); } /** * Grow the dequeue by doubling its size. * A new array is created, all the elements in the old array * are copied in the first half of the new array */ @SuppressWarnings("unchecked") void grow() { // TODO } } // --------------------------------------------------------- class DequeueArrayOneAndHalf extends DequeueArray { DequeueArrayOneAndHalf (int initialCapacity) { super(initialCapacity); } /** * Grow the dequeue by multiplying its size by 1.5 and rounding * A new array is created, all the elements in the old array * are copied in the first half of the new array */ @SuppressWarnings("unchecked") void grow() { // TODO } } // --------------------------------------------------------- class DequeueArrayPlusOne extends DequeueArray { DequeueArrayPlusOne (int initialCapacity) { super(initialCapacity); } /** * Grow the dequeue by one * A new array is created, all the elements in the old array * are copied in the first part of the new array */ @SuppressWarnings("unchecked") void grow() { // TODO } }