What is the difference between null, 0 and nothing?

Question

What is the difference between null, 0 and nothing?

I cannot find a question addressing all three of these.

For example:

If I am getting input from a string and parsing it to int.

return Integer.parseInt(sc.nextLine());

Or if I am asking if a string != "", or a is not nothing I am confused about which to use when and why.

I am confused about which one to use when validating data.

score 16 · Accepted Answer · answered Oct 29 '13 at 09:18

16

null means that a variable contains a reference to a space in memory that does not contain an object.

0 is a numeric data type with a value of 0.

Nothing doesn't really exist, however I think you may be viewing this as an empty String "" which is simply a String data type that does not contain a value.

If your looking at this from a Javascript paradigm it may be confusing. In Java variables are not truthy and falsey therefore the type is considered in comparisons.

answered Oct 29 '13 at 09:18

Kevin Bowersox

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In Java `void` just indicates that a method does not return an object or primitive. – Kevin Bowersox Oct 29 '13 at 09:25
is null equals with NULL? – koding Mar 12 '20 at 23:48

Ingo · Answer 2 · 2013-10-29T09:32:21.500

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0 is a number, you use it to check if a numeric value (int, short, float, double, etc.) is the number 0.

null is the value of a reference that points nowhere, you use it to make sure a reference does indeed reference something.

nothing is not part of Java.

The closest thing for nothing (for: no information at all) is the void declaration of a method. It states that the method returns literally nothing.

Note that 0, null and the empty string "" are values and thus contain information.

For example, 0 is the answer to "What is 5 subtracted from 5?" (among others).

null is the negative response to "Does this thing point to an object?".

""" could be the answer to "What is the longest sequenc of 'X's in your name?", unless your name is "Xanthippe".

edited Oct 29 '13 at 09:32

answered Oct 29 '13 at 09:16

Ingo

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Yes, it declares that a method (and only methods can be void) is not going to return anything. But you can't check if some value is void, hence it is in a different category with 0 and `null`, which are values. – Ingo Oct 29 '13 at 09:27
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Updated my answer to include `void`. – Ingo Oct 29 '13 at 09:32

Dan D. · Answer 3 · 2013-10-29T09:20:14.720

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There isn't a "nothing" in Java. There is a null reference, meaning that a variable refers to no object, so it is a kind of nothing, but there isn't the concept of undefined as it is in Javascript.

Also, please note that a String comparison should be done using equals, not != or ==, so string.equals(otherString).

The 0 value is the default value that an int gets when declared as an instance variable.

edited Oct 29 '13 at 09:20

answered Oct 29 '13 at 09:15

Dan D.

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@Skippy `undefined` (in JS) is as much of a something (or "nothing") as `null` is. It is a sentinel value. Now, `void` in Java represents nothing .. and their is no value which can satisfy it. – user2864740 Oct 29 '13 at 09:17
"The 0 value is the default value that an int gets when declared." No, no, no! – Ingo Oct 29 '13 at 09:18
@Ingo Why not? int x; What is the value of x if you print it? – Dan D. Oct 29 '13 at 09:18
In a method? Try it, Dan. – Ingo Oct 29 '13 at 09:19
I didn't say anything about a method, but I added something to make sure it is not interpreted. – Dan D. Oct 29 '13 at 09:20
You did say "when declared". In a method, `int x;` is a declaration of an int, is it not? – Ingo Oct 29 '13 at 09:20

score 5 · Answer 4 · answered Oct 29 '13 at 09:18

"Null" in Java , the object reference is not pointing to any object, it is null.

"Nothing", Java has nothing called "Nothing"

"0" means that .the string object exists with a value of "0"

"" means an empty String ,i.e the String Object exists with value ""

score 5 · Answer 5 · edited Dec 18 '18 at 06:36

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"nothing" means nothing in Java.
0 means an integer value greater than -1 and less than 1.
"Null" means if any Object Reference points nowhere in the memory, then it's called "Null" reference.

edited Dec 18 '18 at 06:36

Pang

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answered Oct 29 '13 at 09:18

dg_no_9

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score 3 · Answer 6 · edited Dec 18 '18 at 06:35

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The best approach to check String objects in Java is using org.apache.commons.lang.StringUtils.

If you do not want to use StringUtils, you might want to check that sc.nextList() is not null (!= null) first of all, if it is not null then you can check that is different from "" (!= "").

edited Dec 18 '18 at 06:35

Pang

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answered Oct 29 '13 at 09:19

alexgrimaldi

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score 2 · Answer 7 · edited Dec 18 '18 at 10:18

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For example:

int s;      //s=null
int s = 0 ;  //s=0
String s="";// s=nothing

edited Dec 18 '18 at 10:18

Pang

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answered Oct 29 '13 at 09:17

Foster Hao

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int cannot be NULL!!! NEVER NEVER NEVER! NULL is an object value which reference that the object does not have an memory allocation! (This post tagged with java) – BananaBuisness Dec 12 '15 at 15:15
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The empty string is not nothing. It is a perfect valid string value, which plays a role very similar to 0 in the realm of natural numbers. For example, both "" and 0 are neutral elements for some operation (both named +). – Ingo Dec 22 '18 at 02:06

Kamran · Answer 8 · 2017-02-06T09:37:34.253

Null variable isn't assigned any value. The memory space (of variable) is empty or holds garbage value. while a variable is 0, the variable holds the value '0'. The memory space has value '0' stored in it.

NULL basically means no value, or unknown,NULL value could be either empty, meaningless, or not even initialized. For eg when we say, Employee bonus is null, it means the person is not getting any bonus or not eligible for bonus.now in case if value is 0 its mean employee getting bonus but currently bonus is zero.

What is the difference between null, 0 and nothing?

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