String constant pool query

Question

public class D2 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        String s1="java";
        String s2="ja".concat("va");
        System.out.println(s1==s2);
    }
}

On concatenating two String constants in s2 doesn't result in a new String object(String objects are only created when new is used or a perm reference like s1 on concatenation). Kindly shed light on why the o/p is false.

http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java?lq=1 that might help — KonradOliwer, May 13 '14 at 08:01
concat is the runtime statement, the compiler can not tell the result of runtime statetement when it compiles the code, so, the new "java" will be the new String, not the same from string pool — VinhNT, May 13 '14 at 08:01

score 4 · Answer 1 · answered May 13 '14 at 08:00

On concatenating 2 String constants in s2 doesn't result in a new String object

That's true when it's performed with the string concatenation operator - but that's not what you're doing here. You're manually calling String.concat, so this is not a constant expression, and not evaluated at compile time.

If you used:

String s2 = "ja" + "va";

then the concatenation would be performed by the compiler, and s1 and s2 would refer to the same object.

JLS section 15.28 gives details around what leads to a constant expression, and that doesn't include method calls.

You are the fastest JLS quoter ever. – Maroun May 13 '14 at 08:03 — Maroun, May 13 '14 at 08:03

String constant pool query

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