1 简单工厂模式

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;
        }
        return oper;
    }
}

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;

        }

        return oper;

    }

}