Error while attempting null check

Question

I am checking for null before doing a certain operation but I have run into some issues. Following is the code:

if (c != null && c.size() != null) {
    if (c.size() > 0) {
        return (Application) c.toArray()[0];
}

I am getting a 'The operator != is undefined for the argument type(s)int, null' at the point c.size() != null. I understand the return type for the size method is an integer, is that why I am getting this error? Hope someone can advise. Thank you.

`int` is a primitive type, and doesn't have `null` that is why is complaining so that condition is unnecesary. In fact as is not a reference to an object it can't be null. — nachokk, Mar 24 '14 at 03:34
c.size() returns an int. You cannot compare an int(primitive type) with null. Also, the inner if(c.size()>0) is also redundant as you ahve already done the size check in the previous if statement. — TheLostMind, Mar 24 '14 at 03:34
learn more about [primitive datatype](http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html) `.size` will never return `null`, the default value of `int` is `0`. so you should change `null` to `0` — Baby, Mar 24 '14 at 03:41

score 0 · Answer 1 · edited May 23 '17 at 10:31

0

int is a primitive type and is not an Object so is not a reference that can be null. Read more in this previous answer

Then in your code just remove that condition. And also is preferred you use c.isEmpty() rather than c.size()>0

Your code would look like this:

if (c != null && !c.isEmpty()) {
    return (Application) c.toArray()[0];
}

edited May 23 '17 at 10:31

Community

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answered Mar 24 '14 at 03:38

nachokk

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Hi, if c happens to be null, that would mean it's also empty right? – John Java Mar 24 '14 at 07:38
@JohnJava Not, if `c` is null means that the reference `c` is not pointing to any object, so if you make `c.isEmpty()` will throw `NullPointerException` – nachokk Mar 24 '14 at 19:44
Thanks nachok, what about a scenario like this List list and I do a if if (list != null), there would not be a need for me to also do a list.isEmpty() right? since list in this case is an obj ref variable. – John Java Mar 26 '14 at 02:08
@JohnJava No!! `list` is just a reference(like a pointer) that refers to an Object of Type(LIST), if it's not pointing to anywhere then `list` is null, but if it's pointing to a `List` then could be empty or not. – nachokk Mar 26 '14 at 02:15

score 0 · Answer 2 · answered Mar 24 '14 at 03:39

First of all, the result of c.size() is an integer. An int is a primitive, and it cannot be null. Only objects can be null.

Second, c.size() will never return null, so the check

c.size() != null

is unnecessary.

Note: There are wrapper classes for each primitive type. For example

Integer i = 4;
i = null; // valid

That assignment will be valid because i is an instance of the class Integer.

Error while attempting null check

2 Answers2