X1010: Keep Evens

Use this interface definition to solve this problem.

public interface QueueADT<E> {
  /* Set the queue to its initial state. */
  public void clear();

  /* Add an element to the queue (on rear). */
  public boolean enqueue(E it);

  /* Remove the element from front of the queue and
     return it. */
  public E dequeue();

  /* Returns the element from front of the queue without
   * removing it. */
  public E frontValue();

  /* Return the number of elements in the queue. */
  public int numElements();

  /* Is the queue empty? */
  public boolean isEmpty();
}

Write a method to given a queue, keeps only the even values in the queue. Note that you can't access the whole queue, you have to dequeue() one at a time and if it is an even number, then put it back in the queue. If it is not, then ignore it, thus dicarding it. If queue is null, it should do nothing.

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