public class X { public static void main(final String[] args) { String s1 = "123"; StringBuffer s2 = new StringBuffer(s1); if (s1.equals(s2)) { System.out.println("s1 equals to s2"); } else if (s2.equals(s1)) { System.out.println("s2 equals to s1"); } else { System.out.println("not equal."); } } }A) Compiler error.