Does java optimize string literal toLowerCase()?

Question

Does java optimize operations with string literals? For example, does

\"literal\".toLowerCase()

always create a new string instance?

Answer 1

First of, I think that is unspecified, so the behavior might differ between JDKs.

However, in my Oracle JDK 1.8.0_131, when I look at the source code of String.toLowerCase(Locale), I see that there is a check that returns the string itself, if no characters need to be changed.

/* Now check if there are any characters that need to be changed. */
scan: {
    for (firstUpper = 0 ; firstUpper < len; ) {
        // Basically
        if(characterNeedsToBeChanged) {
            break scan;
        }
    }
    return this;
}
...
// Create a new string
....