我可以将String映射到Java中的方法吗? [英] Can I map a String to a method in java?

问题描述

我正在用Java编写一个表达式评估器.我想要添加更多运算符的能力(我目前只有(，)，+，-，*，/和^).目前，我的代码如下:

I'm writing an expression evaluator in Java. I would like the ability to add more operators (I currently have only (, ), +, -, *, /, and ^). Currently, my code looks like this:

case '+':  
return a+b;  
case '-':  
return a-b;  
case '*':  
return a*b;  
...

这对我的代码有效，因为我只有几个运算符.但是，如果我要添加更多运算符，则代码将变得混乱.我正在寻找一种将运算符(由String表示)映射到方法的方法.例如，"ln"将映射到Math.log()，"^"将映射到Math.pow()，等等.

This works for my code because I have only a few operators. However, if I were to add more operators, the code would become cluttered. I am looking for a way to map an operator (represented by a String) to a method. For example, "ln" would be mapped to Math.log(), "^" would be mapped to Math.pow(), etc.

我将如何去做?如果不可行，有什么替代方法?

How would I go about doing this? If it's not feasible, what are some alternatives?

推荐答案

除非您要使用反射，否则不可能.没有反射的解决方案可能看起来像这样:

Not possible unless you want to use reflection. A solution without reflection could look like this:

public interface Operation {
  int apply(int... operands);
}

public abstract class BinaryOperation implements Operation {
  @Override
  public int apply(int... operands) {
    return apply(operands[0], operands[1]);
  }

  abstract int apply(int a, int b);
}

Map<String, Operation> operations = new HashMap<String, Operation>() {{
  put("+", new Operation() {
    @Override
    public int apply(int... operands) {
      return operands[0] + operands[1];
    }
  });
  put("-", new BinaryOperation() {
    @Override
    public int apply(int a, int b) {
      return a - b;
    }
  });
}};

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