So what makes String literals so special? Well, first of all, it's very important to remember that String objects are immutable. That means that, once created, a String object cannot be changed (short of using something like reflection to get at private data). Immutable, you say? Unchangable? What about this code?

via https://www.javaranch.com/journal/200409/ScjpTipLine-StringsLiterally.html.