/**
     * Adds an item to this collection.
     * @param x any object.
     * @return true if this item was added to the collection.
     */
    public boolean add( AnyType x )
    {
        int currentPos = findPos( x );
        if( isActive( array, currentPos ) )
            return false;
       
        if( array[ currentPos ] == null ) 
            occupied++;
        array[ currentPos ] = new HashEntry( x, true );
        currentSize++;
        modCount++;
        
        if( occupied > array.length /  2  )        
            rehash( );
                
        return true;                   
    }

    /**
     * Method that performs quadratic probing resolution.
     * @param x the item to search for.
     * @return the position where the search terminates.
     */
    private int findPos( Object x )
    {
        int offset =  1 ;
        int currentPos = ( x == null ) ?  0  : Math.abs( x.hashCode( ) % array.length );

        while( array[ currentPos ] != null )
        {
            if( x == null )
            {
                if( array[ currentPos ].element == null )
                    break;
            }
            else if( x.equals( array[ currentPos ].element ) )   
                break; 
            
            currentPos += offset;                  // Compute ith probe
            offset +=  2 ;
            if( currentPos >= array.length )       // Implement the mod
                currentPos -= array.length;
        }

        return currentPos;
    }