Question

I read that in Java, String is immutable, so we can’t really use toLowerCase intuitively, i.e the original string is unmodified:

String s = "ABC";
s.toLowerCase();

> "ABC"

But even using StringBuffer(which supports mutable Strings) does not work

StringBuffer so = new StringBuffer("PoP");

so.toLowerCase()

> Static Error: No method in StringBuffer has name 'toLowerCase'

I appreciate any tips or advice.

Answer 1

Well, it doesn’t. You’d have to use .toString().toLowerCase():

String lowercase = sb.toString().toLowerCase();

If you want to be very strict about not creating unnecessary instances, you can iterate all characters, and lowercase them:

for (int i = 0; i < sb.length(); i++) {
   char c = sb.charAt(i);
   sb.setCharAt(i, Character.toLowerCase(c));
}

And finally – prefer StringBuilder to StringBuffer