package rebelsky.linear;

/**
 * An implementation of queues using arrays.  Currently incomplete,
 * as it fails when the array fills.
 *
 * @author Samuel A. Rebelsky
 * @version 1.0 of October 2004.
 */
public class ArrayBasedQueue
	implements Queue
{
// +--------+--------------------------------------------------
// | Fields |
// +--------+

	/** The index of the "last" thing. */
	int last;

	/** The index of the "first" thing. */
	int first;

	/** The stuff actually in the stack. */
	Object[] contents;

// +--------------+--------------------------------------------
// | Constructors |
// +--------------+
	
	public ArrayBasedQueue()
	{
		this.last = -1;
		this.first = 0;
		this.contents = new Object[10];
	} // ArrayBasedQueue()

// +---------+-------------------------------------------------
// | Methods |
// +---------+

	public void put(Object addMe)
	{
		this.last = this.last + 1;
		// Have we run out of space?  If so, shift left.
		if (this.last == this.contents.length) {
			for (int i = this.first; i < this.contents.length; i++) {
				this.contents[i-this.first] = this.contents[i];
				this.contents[i] = null;
			} // for
			this.last = this.last - this.first;
			this.first = 0;
		} // if
		this.contents[this.last] = addMe;
	} // put(Object)

	public Object get()
		throws Exception
	{
		if (this.contents[this.first] == null)
			throw new Exception("It's empty!");
		Object returnMe = this.contents[this.first];
		this.contents[this.first] = null; // Actually remove it.
		++this.first;
		return returnMe;
	} // get()

	public Object peek()
	{
		return this.contents[this.first];
	} // peek()

	public boolean isEmpty()
	{
		return this.contents[this.last] == null;
	} // isEmpty()

} // class ArrayBasedQueue