Difference between NULL and empty string

[Vijay jai Singh]

Hi,

What is difference between null string (String abc = null) and empty string (String abc = "")

Thank you
Vijay

[Ankit Garg]

Try to call a method on both of them and you'll see the difference

String s = "";
s.length();

String s = null;
s.length();

Basically a reference to an empty string points to an object in the heap so you can call methods on it. But a reference pointing to null has no object to point in the heap and thus you'll get a NullPointerException...

[leroy tsruya]

hi vijai,

when you declare

 
String s = "" ;
   

you actually declare a new String Object, and it means the variable (in this case - s) has a String Object associated to it. you can call String methods on that object.
it is like typing:

  
String s = new String();
  

if you type:

   
String s = "";
s.lentgh; // return 0
 

however, when you declare

   
String s = null;
 

null means that the variable (the reference pointer) is empty. it is not pointing to any Object at all.
in that case if you type:

 
String s = null;
s.lentgh;//returns a null pointer exception
   

hope it helps!

[Ankit Garg]

leroy tsruya wrote:

   
String s = "";
s.lentgh; // return 0
 

This will not compile. The length (which you wrote as lentgh ) is not a property, its a method, so use s.length()...

[Rahul P Kumar]

Seeing above replies now you know that in null case there is no object created and currently variable is pointing to nothing, while in later case, there is an empty string object created and variable is pointing to that. Now you take println in both cases and see what it prints.

[leroy tsruya]

wow im such a dumb.. of course its a method....

[Campbell Ritchie]

Think nothing of it; we all make that sort of mistake.

And there is another spelling error; it should read null not NULL in the thread title. Remember Java is case-sensitive and you can get all sorts of difficult-to-find errors if you put a capitaL letter in the wrong place.

[fred rosenberger]

I think of an empty string ("") as a box that is empty.

a null string means you don't even have a box!!!

In all cases, you can refer to "the box that holds my comic books". The box may not exist, the box may exist but be empty, or the box may be full.

[Rahul P Kumar]

ok you take print of string in case it is null, it still prints your box. What is that? What is null?

[Henry Wong]

Rahul.p Kumar wrote:ok you take print of string in case it is null, it still prints your box. What is that? What is null?

No it doesn't "print your box". There is a special check in the print to see if it is null, and replaces it with "null", so it can be printed.

Or to stay with the metaphor... when you ask your friend to tell you what's in the box, he will tell you what is in the box, but if there is no box, will tell you that there is no box.

Henry

[Rahul P Kumar]

thanks for this insight.