Question

one thing that i always wondered, if i have a method like this:

String replaceStuff (String plainText) {
        return plainText.replaceAll("&", "&");
}

will it create new String objects all the time for the “&” and the “&” that gets destroyed by the GC and then recreated again by next call?
E.g.
would it in theory be better to do something like this

final String A ="&";
final String AMP ="&";

    String replaceStuff (String plainText) {
            return plainText.replaceAll(A, AMP);
    }

i think this is probably a more theoretic question than a real life problem, I am just curious how the memory management is handled in this aspect.

Answer 1

No. String literals are interned. Even if you use an equal literal (or other constant) from elsewhere, you’ll still refer to the same object:

Object x = "hello";
Object y = "he" + "llo";

System.out.println(x == y); // Guaranteed to print true.

EDIT: The JLS guarantees this in section 3.10.5

String literals-or, more generally, strings that are the values of constant expressions (§15.28)-are “interned” so as to share unique instances, using the method String.intern.

Section 15.28 shows the + operator being included as an operation which can produce a new constant from two other constants.