Java: The logic of the conditional statement doesn't work and allows the program to run even when the conditions are not met

Question

I have the following two lines of code, where I have set certain conditions for a conditional statement to execute. However, there is something wrong with the logic, because the program inside the conditional runs even when the conditions are not met.

if (!(token.equals('+')) && !(token.equals('-')) && !(token.equals('*')) && !(token.equals('/'))) {
            operandStack.push(Integer.valueOf(token));
        }

I am getting a java.lang.NumberFormatException: For input string: "whatever operator (+,-,* and /) that I enter in my test case" in the second line of this code and I realize that it's because Integer.valueOf() doesn't work for symbols, but that's the thing. If it's a symbol, it shouldn't be executing in the first place. I have tried looking for all kinds of typos or stupid syntax mistakes, but haven't found any. What's wrong with this logic?

Answer 1

You might do better to check if the token is an integer via a regular expression:

if (token.matches("\\d+")) {
    operandStack.push(Integer.parseInt(token));
}

And then parse the string into an integer.

The pattern \\d+ (double escaped for Java) matches on one or more digits.