Difference in Null and Empty String

Question

Hi,
I have been wondering about the difference between Null and Empty String in Java. So I wrote a small program like this:
public class CompareEmptyAndNullString {
     public static void main(String args[]) {
          String sNull = null;
          String sEmpty = "";
          try {
               if (sNull.equalsIgnoreCase(sEmpty)) {
                    System.out.println("Null and Empty Strings are Equal");
               } else {
                    System.out.println("Null and Empty Strings are Equal");
          } catch (Exception e) {
               e.printStackTrace();
This program throws Exception: java.lang.NullPointerException
     at practice.programs.CompareEmptyAndNullString.main(CompareEmptyAndNullString.java:10)
Now if I change the IF Clause to if (sEmpty.equalsIgnoreCase(sNull)) then the Program outputs this: Null and Empty Strings are Equal
Can anyone explain why this would happen ?
Thanks in Advance !!

Answer 1

JavaProwler wrote:
Saish,
Whether you do any of the following code, the JUnit Test always passes: I mean he NOT Sign doesnt make a difference ...
assert (! "".equals(null));
assert ("".equals(null));
You probably have assertions turned off. Note the the assert keyword has nothing to do with JUnit tests.
I think that older versions of JUnit, before assert was a language keyword (which started in 1.4 or 1.5), had a method called assert. Thus, if you have old-style JUnit tests, they might still compile, but the behavior is completely different from what it was in JUnit, and has nothing to do with JUnit at all.
If you turn assertions on (-ea flag in the JVM command line, I think), the second one will throw AssertionError.