Differnce between null string and an empty string??

Question

what is the major difference between null string and an empty string??
I wrote the following simple program and I could see some different output.
Other than that, any other differences that we should pay attention to???
C:\>java TestCode
Hello
nullHello
public class TestCode
     public static void main(String[] s)
     {     String s1 = "";
          String s2 = null;
          System.out.println(s1 + "Hello");
          System.out.println(s2 + "Hello");
}

Answer 1

There's a big difference between the two. A null String isn't pointing to an object, but an empty String is. For example, this is perfectly fine:
public class TestCode
    public static void main(String[] args)
        String s = "";
        System.out.println(s.length());
} It prints out 0 for the length of the String, just as it should. But this code will give you a NullPointerException:
public class TestCode
    public static void main(String[] args)
        String s = null;
        System.out.println(s.length());
} Since s isn't pointing to anything, you can't call its methods.