Java: replaceAll doesn't work as I think it should

Question

public class NewClass {
    public static void main(String[] args) {
            String piece = "10*2";
            String ans = "20";
            String problm = "10*2*9";

            System.out.println(piece);
            System.out.println(ans);

            problm.replaceAll(piece, ans);

            System.out.println(problm);
    }
}

This is my code, and when I print problm it prints: 10*2*9 I want it to print 20*9, please tell me what I'm doing wrong

Answer 1

First of all, use replace instead of replaceAll. replaceAll uses regular expressions, which you probably don't want.

Secondly, Strings in Java are immutable, meaning that their value can never be changed. You need to assign the value of problm.replaceAll(piece, ans); back to problm:

problm = problm.replace(piece, ans);