source: src/main/java/agents/anac/y2011/TheNegotiator/Queue.java

package agents.anac.y2011.TheNegotiator;

/**
 * Array-based implementation of the queue.
 * @author Mark Allen Weiss
 */
public class Queue {
        
    private Double [] theArray;
    private int currentSize;
    private int front;
    private int back;

    private static final int DEFAULT_CAPACITY = 15;   
    
    /**
     * Construct the queue.
     */
    public Queue() {
        theArray = new Double[DEFAULT_CAPACITY];
        makeEmpty( );
    }


    /**
     * Test if the queue is logically empty.
     * @return true if empty, false otherwise.
     */
    public boolean isEmpty() {
        return currentSize == 0;
    }

    /**
     * Make the queue logically empty.
     */
    public void makeEmpty() {
        currentSize = 0;
        front = 0;
        back = -1;
    }

    /**
     * Return and remove the least recently inserted item
     * from the queue.
     * @return the least recently inserted item in the queue.
     * @throws UnderflowException if the queue is empty.
     */
    public Double dequeue( )
    {
        currentSize--;

        Double returnValue = theArray[front];
        front = increment( front );
        return returnValue;
    }
    
    /**
     * Get the least recently inserted item in the queue.
     * Does not alter the queue.
     * @return the least recently inserted item in the queue.
     * @throws UnderflowException if the queue is empty.
     */
    public Double getFront( )
    {
        return theArray[ front ];
    }

    /**
     * Insert a new item into the queue.
     * @param x the item to insert.
     */
    public void enqueue( Double x )
    {
        if( currentSize == theArray.length )
            doubleQueue( );
        back = increment( back );
        theArray[ back ] = x;
        currentSize++;
    }

    /**
     * Internal method to increment with wraparound.
     * @param x any index in theArray's range.
     * @return x+1, or 0 if x is at the end of theArray.
     */
    private int increment( int x )
    {
        if( ++x == theArray.length )
            x = 0;
        return x;
    }
    
    /**
     * Internal method to expand theArray.
     */
    private void doubleQueue( )
    {
        Double [ ] newArray;

        newArray = new Double[ theArray.length * 2 ];

            // Copy elements that are logically in the queue
        for( int i = 0; i < currentSize; i++, front = increment( front ) )
            newArray[ i ] = theArray[ front ];

        theArray = newArray;
        front = 0;
        back = currentSize - 1;
    }

        public int size() {
                return currentSize;
        }

        /**
         * @return array of queue (watch out, contains empty cells)
         */
        public Double[] toArray() {
                return theArray;
        }
}