What is the output displayed? : Questions « Operators « SCJP

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public class MainClass {
  public static void main(String[] args) {
    String s1 = "ab";
    String s2 = "ab";
    String s3 = "cd";
    String s4 = s1 + s3;
    s1 = s4;
    System.out.print("s1 " + ((s1 == s2) ? "==" : "!=") + " s2");
  }
}