import java.util.NoSuchElementException;

/**
 * The definition of the Queue interface
 * 
 * @param <Q>
 * @author gtowell Modified Feb 14 2020
 */
public interface QueueIntf<Q> {
    /**
     * The number of items in the queue
     * 
     * @return the number of items in the queie
     */
    int size();

    /**
     * Return true iff the queue is empty
     * 
     * @return true iff the queue is empty
     */
    boolean isEmpty();

    /**
     * Inserts the specified element into this queue if it is possible to do so
     * immediately without violating capacity restrictions, returning true upon
     * success and throwing an IllegalStateException if no space is currently
     * available.
     * 
     * @param q the element to be added
     * @return true
     * @throws IllegalStateException if the element cannot be added at this time due
     *                               to capacity restrictions
     */
    boolean add(Q q) throws IllegalStateException;

    /**
     * Retrieves and removes the head of this queue. This method differs from poll
     * only in that it throws an exception if this queue is empty.
     * 
     * @return the removed element, if such an element exists
     * @throws NoSuchElementException if this queue is empty
     */
    Q remove() throws NoSuchElementException;

    /**
     * Retrieves, but does not remove, the head of this queue. This method differs
     * from peek only in that it throws an exception if this queue is empty.
     * 
     * @return the element at the head of the queue
     * @throws NoSuchElementException if this queue is empty
     */
    Q element() throws NoSuchElementException;

    /**
     * Inserts the specified element into this queue if it is possible to do so
     * immediately without violating capacity restrictions, returning true upon
     * success and false on failure
     * 
     * @param q the element to be added
     * @return true on success, false on failure
     */
    boolean offer(Q q);

    /**
     * Retrieves and removes the head of this queue. This method differs from poll
     * only in that it throws an exception if this queue is empty.
     * 
     * @return the removed element, or null if the queue is empty
     */
    Q poll();

    /**
     * Retrieves, but does not remove, the head of this queue. This method differs
     * from peek only in that it throws an exception if this queue is empty.
     * 
     * @return the element at the head of the queue or null if the queue is empty
     */
    Q peek();
}