String constant pool query

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.

Jon Skeet
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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.

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