QueueInterface.java (1457B)
1 package lab6; 2 3 public interface QueueInterface<T> { 4 5 public boolean isEmpty(); 6 // Determines whether a queue is empty. 7 // Precondition: None. 8 // Postcondition: Returns true if the queue is empty; 9 // otherwise returns false. 10 11 public void enqueue(T newItem) throws QueueException; 12 // Adds an item at the back of a queue. 13 // Precondition: newItem is the item to be inserted. 14 // Postcondition: If the operation was successful, newItem 15 // is at the back of the queue. Some implementations 16 // may throw QueueException if newItem cannot be added 17 // to the queue. 18 19 public T dequeue() throws QueueException; 20 // Retrieves and removes the front of a queue. 21 // Precondition: None. 22 // Postcondition: If the queue is not empty, the item that 23 // was added to the queue earliest is removed. If the queue is 24 // empty, the operation is impossible and QueueException is thrown. 25 26 public void dequeueAll(); 27 // Removes all items of a queue. 28 // Precondition: None. 29 // Postcondition: The queue is empty. 30 31 public T peek() throws QueueException; 32 // Retrieves the item at the front of a queue. 33 // Precondition: None. 34 // Postcondition: If the queue is not empty, the item 35 // that was added to the queue earliest is returned. 36 // If the queue is empty, the operation is impossible 37 // and QueueException is thrown. 38 39 public String toString(); 40 } // end QueueInterface 41