No. When and how strings are intern
ed is described in the String#intern
documentation and the JLS Section 3.10.5. Basically, literals and (other) string constants are auto-interned, but nothing else is likely to be unless you do it explicitly.
As a side point, you seem to be assuming that interned strings are never garbage-collected. I don't see anything in the Java documentation actually saying that, and at least one person claims that his tests show that they are, in fact, GC'd, suggesting that the intern pool uses some form of weak reference.