public class OperationFactory{    public static Operation createOperate( string operate)    {        Operation oper = null;        switch (operate)        {			case “+”:				oper = new OperationAdd();				break;			case “-”:				oper = new OperationSub();				break;			case “*”:				oper = new OperationMul();				break;			case “/”:				oper = new OperationDiv();				break;        }     }}