//********************************************************************
//  Demonstrates the use of a user-defined Queue class.
//********************************************************************

public class UseQueue
{
   public static void main (String[] args)
   {  
      Queue word = new Queue();

      //adds objects to the queue (of class String here)
      word.enqueue("One");
      word.enqueue("Two");
      word.enqueue("Three");
      

      // take elements out of the queue
       
      while (!word.isEmpty())
            System.out.println (word.dequeue());
    }
}


/* QueueInterface.java */

public interface QueueInterface{
 
  /* isEmpty() returns true if this Queue is empty, false otherwise.*/
  public boolean isEmpty();
  
  /*  enqueue() inserts an object at the end of the Queue.*/
  public void enqueue(Object element);
  
  /*  dequeue() removes and returns the object at the front of
      the Queue.*/
  public Object dequeue();
}


// file Queue.java
import java.util.LinkedList; 
public class Queue implements QueueInterface
{
  private LinkedList queue = new LinkedList(); 
  public void enqueue(Object obj) 
  { // Add an item to back of queue. 
     queue.addLast(obj); 
  } 
  public Object dequeue() 
   { // Remove the next item from the front of the queue. 
     // (Note that queue.removeFirst() both removes an  item from the list, and returns the item that 
     // was removed.)
      return queue.removeFirst(); 
     } 
     
  public boolean isEmpty() 
     { // Test if the queue is empty. 
       return queue.isEmpty(); 
      } 
 } // end class Queue