Difference between null and empty string [duplicate]

Question

What is the difference between a null string (String s = null) and an empty string (String s = "")?

This is what I have:

String s1 = ""; //print statement does not print any thing for s1 but s1.length()=0 String s2 = null;//print statement prints "null" for s2  but s2.length() gives exception 

What does it mean?

Answer 1

String s1 = ""; means that the empty String is assigned to s1. In this case, s1.length() is the same as "".length(), which will yield 0 as expected.

String s2 = null; means that (null) or "no value at all" is assigned to s2. So this one, s2.length() is the same as null.length(), which will yield a NullPointerException as you can't call methods on null variables (pointers, sort of) in Java.

Also, a point, the statement

String s1; 

Actually has the same effect as:

String s1 = null; 

Whereas

String s1 = ""; 

Is, as said, a different thing.