Strings Are Immutable

As you look over the documentation of the String methods, you might notice toUpperCase and toLowerCase. These methods are often a source of confusion, because it sounds like they have the effect of changing (or mutating) an existing string. Actually, neither these methods nor any others can change a string, because strings are immutable.

When you invoke toUpperCase on a String, you get a new String as a return value. For example:

After the second line is executed, upperName contains the value "ALAN TURING", but name still contains "Alan Turing".