class MainClass {
public static void main(String[] args) {
String s1 = "abc";
String s2 = "abc";
String s3 = "def";
if (s1 == s2)
System.out.println("s1 == s2");
if (s1 != s3)
System.out.println("s1 != s3");
if (s2 != s3)
System.out.println("s2 != s3");
String s4 = s1.toUpperCase();
if (s4 != s1)
System.out.println("s4 != s1");
System.out.println("s1 = " + s1);
System.out.println("s4 = " + s4);
}
}