public int compare(Object a, Object b) throws ClassCastException
	    {
        	if(a == null){
        		return -1;
        	}
        	else if(b == null){
        		return 1;
        	}
        	else if(a == null && b == null ){
        		return 0; 
        	}
        	else{
	            MessageBid bida = (MessageBid) a;
	            MessageBid bidb = (MessageBid) b;

	            Double d_c1 = new Double( bida.getPrice());
	            Double d_c2 = new Double( bidb.getPrice());

	            return d_c2.compareTo(d_c1);
        	}
	 	}