Question

I am making a calculator and part of this program takes in user String input and tokenizes it (using my own implementation of a Tokenizer class). So now I have a bunch of Token objects and I would like to test each one of them to see if they hold numbers or operators.

Is there a way to test to see if they hold operators (ie. +, -, *, /, =, (, ), etc.) without using
if (token.equals("+") || token.equals("-") || ... and so on, for each operator? These Token objects are all of type String.

Answer 1

If they’re all single-character strings you can do:

if ("+-*/=()".indexOf(token) > -1) {

    // if you get into this block then token is one of the operators.

}

You could use an array to hold values that indicate the precedence of the corresponding token, too:

int precedence[] = { 2, 2, 3, 3, 1, 4, 4 };  // I think this is correct

int index = "+-*/=()".indexOf(token); 
if (index > -1) {

    // if you get into this block then token is one of the operators.
    // and its relative precedence is precedence[index]

}

But since this all assumes that the operator is only one character, this is about as far as you can take this approach.