> Moreover, a string literal always refers to the same instance of class String. This is because 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.
And later:
> Literal strings within different classes in different packages likewise represent references to the same String object.
Source: https://docs.oracle.com/javase/specs/jls/se8/html/jls-3.html...
But that does - as far as I can see - say nothing for non-literal strings.
[edit]: formatting
Nothing much to think -- distinct objects must have distinct references [e.g. new String("a")!=new String("a')], literals must have the same references for the same values [e.g. "a"=="a"].
if("abc" == "abc") { System.out.println("correct"); }
if(new String("abc") != new String("abc")) { System.out.println("correct"); }