Trying to check if a string is Palindrome but concatenation is NOT working

I have below code where the uncommented line in loop is not working as the commented line to check if it is palindrome.

String s = "madam";
String reversed = "";
for (int i = s.length() - 1; i >= 0 ; i--) {
            reversed.concat(Character.toString(s.charAt(i)));
//          reversed += s.charAt(i);
}
return s.equals(reversed)

>Solution :

As @Mirek Pluta hinted in the comments:

You should reassign reversed to the result of reversed.concat(...)

for (int i = s.length() - 1; i >= 0 ; i--) {
    reversed = reversed.concat(Character.toString(s.charAt(i)));
}

Note that reversed += s.charAt(i); is effectively the same as reversed = reversed + s.charAt(i);.