没有if/else或switch的计算器

Question

我试图+ - * /无条件地写计算器.运算符存储为字符串.

反正有没有实现它？

public class Main {

    /**
     * @param args
     */
    public static void main(String[] args) {
        ////String Operator = "";
        String L1="";
        String L2="";
        String op = "+";
        double a = 3;
        double b = 2;

        //Operator p = p.
        Operator p;
        b = Operator.count(a, op, b);
        System.out.println(b);
    }

    public enum Operator {
        PLUS("+"), MINUS("-"), DIVIDE("/"), MULTIPLY("*");

        private final String operator;

        public static double count(double a,String op,double b) {
            double RetVal =0;
            switch (Operator.valueOf(op)) {
            case PLUS:
                RetVal= a + b;
            case MINUS:
                RetVal= a - b;
            case DIVIDE:
                RetVal= a / b;
            case MULTIPLY:
                RetVal= a * b;
            }
            return RetVal;
        }

        Operator(String operator) {
            this.operator = operator;

        }
        // uniwersalna sta?a grawitacyjna (m3 kg-1 s-2)
    }

}

得到此错误:

线程"main"中的异常java.lang.IllegalArgumentException:No enum const class Main $ Operator.+

有线索吗？

Answer 1

您可以使用策略模式并为每个运算符存储计算策略.

interface Calculation {
  double calculate(double op1, double op2);
}

class AddCalculation implements Calculation {
  double calculate(double op1, double op2) {
    return op1 + op2;
  }
}

//others as well

Map<String, Calculation> m = ...;

m.put("+", new AddCalculation());

在执行期间,您可以从地图中获取计算对象并执行calculate().