//---------------------------------------------------------------------------
// ArrayUnbndQueueFloat.java  by Dale/Joyce/Weems                  Chapter 5
//
// Implements UnboundedQueueInterface with an array to hold queue elements.
//
// Two constructors are provided; one that creates a queue of a default
// original capacity and one that allows the calling program to specify the 
// original capacity.
//
// If an enqueue is attempted when there is no room available in the array, a
// new array is created, with capacity incremented by the original capacity.
//
// AJG version:  MAJOR change *not* generic (since java can't do generic arrays)
//               Should be able to change ALL Float's to any other type
//               Format, enlarge() DOUBLES capacity, if-then-else
//---------------------------------------------------------------------------

package ch05.queues;

public class ArrayUnbndQueueFloat implements UnboundedQueueInterfaceFloat {
    private static final int DEFCAP = 100;  // default capacity
    private Float[] array;                  // array that holds queue elements
    private int numElements = 0;            // number of elements in the queue
    private int front = 0;                  // index of front of queue
    private int rear;                       // index of rear of queue

    public ArrayUnbndQueueFloat(int capacity) {
	array = new Float[capacity];
	rear = capacity - 1;
    }
    public ArrayUnbndQueueFloat() { this(DEFCAP); }
    
    // Double the capacity of the queue
    private void enlarge() {
	// create the larger array
	Float[] larger = new Float[2*array.length];
    
	// copy the array; shifting contents so that front is zero
	for (int i=0; i<numElements; i++)
	    larger[i] = array[(i+front)%array.length];
    
	// update data fields
	array = larger;
	front = 0;
	rear = numElements - 1;
    }

    // Adds element to the rear of this queue.
    public void enqueue(Float element) {
    	if (numElements == array.length) 
	    enlarge();
	rear = (rear + 1) % array.length;
	array[rear] = element;
	numElements++;
    }

    // Throws QueueUnderflowException if this queue is empty;
    // otherwise, removes front element from this queue and returns it.
    public Float dequeue() {       
	if (isEmpty())
	    throw new QueueUnderflowException("Helpful msg.");
	Float ans = array[front];
	array[front] = null;
	// optional: front = (front + 1) % queue.length;
	numElements--;
	return ans;
    }

    public boolean isEmpty() { return (numElements == 0); }
}
// Local Variables:
// compile-command: "cd ../..; javac ch05/queues/ArrayUnbndQueueFloat.java"
// End: