Question

Hello I use 2 different ways to check for a word if its a palindrome or not.. 1 way is hardcoded ( this works as expected ) and the other one I use Stringbuilder for but I always get true and never false as output. I don’t understand why its not working when not hardcoded … here is the code I used for the test. ( the commented variabels work )

      public static void main(String[] args) {

      StringBuilder a = new StringBuilder("did");

      StringBuilder b = a.reverse();


     // String a = "did";
     // String b = "dad";

      if(b.equals(a)) {
          System.out.println("true");
      }
      else {
          System.out.println("false");
      }

      System.out.println(b);
      }

Answer 1

Because, StringBuilder#reverse does in place reversing. So, a.reverse() also changes the value of a.

You can create a copy of your StringBuilder rather.

    StringBuilder a = new StringBuilder("did");
    StringBuilder b = new StringBuilder(a);

    if (b.toString().equals(a.reverse().toString())) {
        System.out.println("true");
    } else {
        System.out.println("false");
    }

You need to use toString() to compare the contents. using equals on StringBuilder instances will compares references.