QueueInterface.java

package master1;

public interface QueueInterface<T> {

	  public boolean isEmpty();
	  // Determines whether a queue is empty.
	  // Precondition: None.
	  // Postcondition: Returns true if the queue is empty;
	  // otherwise returns false.
	   
	  public void enqueue(T newItem) throws QueueException;
	  // Adds an item at the back of a queue.
	  // Precondition: newItem is the item to be inserted. 
	  // Postcondition: If the operation was successful, newItem
	  // is at the back of the queue. Some implementations
	  // may throw QueueException if newItem cannot be added
	  // to the queue.

	  public T dequeue() throws QueueException;
	  // Retrieves and removes the front of a queue.
	  // Precondition: None.
	  // Postcondition: If the queue is not empty, the item that
	  // was added to the queue earliest is removed. If the queue is 
	  // empty, the operation is impossible and QueueException is thrown.

	  public void dequeueAll();
	  // Removes all items of a queue.
	  // Precondition: None.
	  // Postcondition: The queue is empty.

	  public T peek() throws QueueException;
	  // Retrieves the item at the front of a queue.
	  // Precondition: None.
	  // Postcondition: If the queue is not empty, the item
	  // that was added to the queue earliest is returned. 
	  // If the queue is empty, the operation is impossible
	  // and QueueException is thrown.
	  
	  public String toString();
	}  // end QueueInterface