Concatenation of two string in String constant pool in java

Question

Since concatenation of two strings will make new string object in string constant pool so why following code evaluates to No.

public class Main {
    public static void main(String[] args) {
        String s = "abcd";
        String s1 = "ab";
        String s2 = "cd";
        s1 = s1+s2;
        if(s1==s)
            System.out.println("YES");
        else
            System.out.println("No");
            }
}

Answer 1

s1+s2 is not a compile-time constant expression because s1 and s2 aren't final (despite them being assigned compile-time constant values).

As such, the value is computed at runtime: the result is not the same instance as the one in the constant pool, despite the value being the same.