Convert String to operator(+*/-) in java

Question

I am using Stack class to calculate simple arithmetic expressions involving integers, such as 1+2*3.your program would execute operations in the order given,without regardin

Answer 1

Do what Ogen suggested and manually check the operator. A quick shortcut to doing the if, else if .... structure is switch, that is

switch(operand) {
case "*":
      break;
case "+":
      break; 
 .....
 default:
}

Answer 2

Quick solution: Use below code for executing correct javascript Arithmetic expression in java.

    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine se = manager.getEngineByName("JavaScript");        
    try {
        Object result = se.eval(val);
        System.out.println(result.toString());
    } catch (ScriptException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

Answer 3

probably the best way to do it will be equals, but it's best to ignore whitespaces:

i'm not quite sure how you split your string, but for example, if you have a char op and two integer a and b:

String str = op.replace(" ", "");

if(str.equals("*")){
   retVal = a*b;
} else if(str.equals("+")){
   retVal = a+b;
}//etc

Answer 4

Ok, assuming your assignment needs you to use the Stack class and you already have the logic to pick numbers ( including the negative numbers -- that would an operator followed by another operator in all but one cases) and operators and parens, what you could do is as follows.

If you encounter a number, pop the last two elements from your stack. The first item you pop will be an operator and the next will be a number. Evaluate the expression and push it into Stack and continue.

You can ignore the parenthesis. You will also have to handle the case of reading a number or parenthesis the first time.

Answer 5

You will have to manually check and assign the operator. E.g.

if (s.equals("+")) {
    // addition
}