Opgave 1 - ArrayQueue

package queueopgaver;

import java.util.NoSuchElementException;

/**
 * An implementation of a queue as a array.
 */
public class ArrayQueue implements QueueI {
    private Object[] elements;
    private int currentSize;
    private int head;
    private int tail;

    /**
     * Constructs an empty queue.
     */
    public ArrayQueue() {
        final int INITIAL_SIZE = 10;
        elements = new Object[INITIAL_SIZE];
        currentSize = 0;
        head = 0;
        tail = 0;
    }

    /**
     * Checks whether this queue is empty.
     *
     * @return true if this queue is empty
     */
    @Override
    public boolean isEmpty() {
        return currentSize == 0;
    }

    /**
     * Adds an element to the tail of this queue.
     *
     * @param newElement the element to add
     */
    @Override
    public void enqueue(Object newElement) {
        growIfNecessary();
        currentSize++;
        elements[tail] = newElement;
        tail = tail + 1;
    }

    /**
     * Removes an element from the head of this queue.
     *
     * @return the removed element
     */
    @Override
    public Object dequeue() {
        if (currentSize == 0) {
            throw new NoSuchElementException();
        }
        Object removed = elements[head];
        head = head + 1;
        currentSize--;
        return removed;
    }

    /**
     * Grows the element array if the current size equals the capacity.
     */
    public void growIfNecessary() {
        if (currentSize == elements.length) {
            Object[] newElements = new Object[2 * elements.length];
            for (int i = 0; i < elements.length; i++) {
                newElements[i] = elements[head + i];
            }
            elements = newElements;
            head = 0;
            tail = currentSize;
        }
    }

    /**
     * Returns the head of this queue. The queue is unchanged.
     *
     * @return the head element
     */
    @Override
    public Object getFront() {
        if (head < 0) {
            throw new NoSuchElementException();
        }
        return elements[head];
    }

    /**
     * The number of elements on the queue.
     *
     * @return the number of elements in the queue
     */
    @Override
    public int size() {
        return currentSize;
    }
}