// Name:     Bradley Shedd
// Program:  LAB#11
// Date:     December 1, 2010
// Class:    Java1302
// Filename: ArrayQueue.java
// Purpose:  This class is an array-based implementation of
//           the classic FIFO queue interface.      
// ****************************************************************

   public class ArrayQueue implements QueueADT
   {
      private int DEFAULT_SIZE = 5;
      private Object[] elements;
      private int numElements;
      private int front, back;
  
    //---------------------------------------------
    // Constructor; creates array of default size.
    //---------------------------------------------
      public ArrayQueue()
      {
         elements = new Object[DEFAULT_SIZE];
         numElements = 0;
         front = 0;
        back = -1;
      }
  
  
    //---------------------------------------------
    // Puts item on end of queue.
    //---------------------------------------------
      public void enqueue(Object item)
      {
         if (isFull())
            increaseSize();
     
         elements[( back + 1 ) % DEFAULT_SIZE] = item;
     
         back++;
         numElements++;
     
      }
  
  
    //---------------------------------------------
    // Removes and returns object from front of queue.
    //---------------------------------------------
      public Object dequeue()
      {
         if (isEmpty())
            System.err.println("This queue is empty!");
     
         front++;
         numElements--;
     
         return elements [front-1];
      }
  
  
    //---------------------------------------------
    // Returns true if queue is empty.
    //---------------------------------------------
      public boolean isEmpty()
      {
         return numElements==0;
      }
  
  
    //---------------------------------------------
    // Returns true if queue is full, but it never is.
    //---------------------------------------------
      public boolean isFull()
      {
         return numElements==DEFAULT_SIZE;
      }
  
  
    //---------------------------------------------
    // Returns the number of elements in the queue.
    //---------------------------------------------
      public int size()
      {
         return numElements;
      }
  
      private void increaseSize()
      {
         Object [] temp = new Object [ 2 * elements.length];
         for ( int i = 0; i < elements.length; ++i)
            temp [i] = elements [ (i + front)% elements.length];
         elements = temp;
         front = 0;
         back = DEFAULT_SIZE - 1; // assumes front and rear start at 0 and -1
         DEFAULT_SIZE  *= 2;
      }
  
    //---------------------------------------------
    // Returns a string containing the elements of the queue
    // from first to last
    //---------------------------------------------
      public String toString()
      {
         String result = "\n";
         for (int i = front, count=0; count < numElements;
                         i=(i+1)%elements.length,count++)
            result = result + elements[i]+ "\n";
         return result;
           
      }
   }

Homepage