String. Relational operator and odd printing

Question

Hi,
I'm wondering if someone could help me with this puzzlement I have. I've search the forum and I search the tutorial with "string and relation operator" and "string and compare" but I couldn't find any answer.
Basically, I want to make sure that we can't use "<", ">", ">=", and "<=" between two strings because I got compiler error. Tutorial only says to use equals() method but I can't find anything that says "Don't use relational operator such as... !"
Another question I have is I have this test code just to know String more.
<code>
public class Test {
static void compare (String s1, String s2) {
System.out.println ("s1 is = " + s1);
System.out.println ("s2 is = " + s2);
System.out.println (s1 + " == " + s2 + s1==s2); //this line prints "false"
System.out.println (s1 + " != " + s2 + s1!=s2); //this line prints "true"
System.out.println ("s1.equals(s2): " + s1.equals(s2));
public static void main (String args[]) {
compare ("Hello", "huhaha");
compare ("Hello", "hello");
compare ("Hello", "Hello");
</code>
I'm wondering why the line that I commented prints "false" and "true" where I expected to print the value of s1 which is "Hello" and s2 which is "huhaha"?
Sorry if the question seems stupid. I do admit I'm a little slow.
Thank you!

Answer 1

This question is asked all the time on this forum.
Basically, the "==" operator between any two Objects (Strings included) is comparing instances. That is, are the two Objects references to the same "real" instance? If so, it will return true. However, just because two Strings contain the same value does not mean they are the exact same instance. So two different strings which contain the value "XXX" could still have "==" return false. For this reason, it is recommended that (in general) you use "==" and "!=" as it relates to Objects only when comparing them to null (there is only one null).
Instead, use the "equals()" method. There are no "<", "<=", ">", or ">=" operators in relation to Objects. Instead, use the Object's compare() method, if available (which it is for Strings).