当运算符存储在字符串中时执行数学运算

Question

I have 2 integers:

int first= 10;
int second = 20;

and a string representing the operation (one of + , - , / , or * ):

String op = "+";

How can I get the result of 10 + 20 in this example?

Answer 1

I don't recommend this but is funny. in java6

String op = '+';
int first= 10;
int second = 20;
ScriptEngineManager scm = new ScriptEngineManager();
ScriptEngine jsEngine = scm.getEngineByName("JavaScript");
Integer result = (Integer) jsEngine.eval(first+op+second);

go with the switch, but remember to convert the string operator to char as switch don't works with strings yet.

switch(op.charAt(0)){
    case '+':
        return first + second;
        break;
   // and so on..

Answer 2

switch (op.charAt(0)) {
  case '+': return first + second;
  case '-': return first - second;
  // ...
}

Answer 3

you can try the following code. It's object oriented, quite generic, and you can easily extend it to add new operators, including operators with a different number of arguments:

public abstract class Operator {
  public abstract Integer compute(Integer...values);
}

public class Plus extends Operator {
  public Integer compute(Integer...values)   {
    return values[0] + values[1];
  }
}

public class Minus extends Operator {
  public Integer compute(Integer...values)   {
    return values[0] - values[1];
  }
}

public class Multiply extends Operator {
  public Integer compute(Integer...values)   {
    return values[0] * values[1];
  }
}


public class Divide extends Operator {
  public Integer compute(Integer...values)   {
    return values[0] / values[1];
  }
}

Map operatorMap = createOperatorMap();

public Map createOperatorMap() {
  Map<String, Operator> map = new HashMap<String, Operator>();
  map.put("+", new Plus());
  map.put("-", new Minus());
  map.put("*", new Multiply());
  map.put("/", new Divide());
  return map;
}

public int compute(int a, int b, String opString) {
  Operator op = operatorMap.get(opString);
  if (op == null)
    throw new IllegalArgumentException("Unknown operator");
  return op.compute(a, b);
}

Answer 4

public double doMath(int first, int second, char op ){

    switch(op){
    case '+':
        return first + second;
        break;
    case '-':
        return first - second;
        break;
    case '*':
        return first * second;
        break;
    case '/':
        return first / second;
        break;
    default:
        return 0;
    }
}

Answer 5

switch(string){
}

(switch on strings)will be allowed in Java7 . Now you can switch with char

switch(string.charAt(0)){
    case '+' : ...  
}

as mentioned above