Strange String pool behavior

Question

I\'ve got a question of some strange String pool behavior. I\'m using == to compare equal Strings to find out whether they\'re in the pool or not.

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Answer 1

"555" + ""

is a compile-time constant, whereas

giveLiteralString() + ""

isn't. Therefore the former compiles into just the string constant "555" and the latter compiles into the actual method invocation and concatenation, resulting in a fresh String instance.

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Also see JLS §3.10.5 (String Literals):

Strings computed by concatenation at run time are newly created and therefore distinct.