[java] Can an int be null in Java?

Can an int be null in Java?

For example:

int data = check(Node root);

if ( data == null ) {
 // do something
} else {
 // do something
}

My goal is to write a function which returns an int. Said int is stored in the height of a node, and if the node is not present, it will be null, and I'll need to check that.

I am doing this for homework but this specific part is not part of the homework, it just helps me get through what I am doing.

Thanks for the comments, but it seems very few people have actually read what's under the code, I was asking how else I can accomplish this goal; it was easy to figure out that it doesn't work.

The code won't even compile. Only an fullworthy Object can be null, like Integer. Here's a basic example to show when you can test for null:

Integer data = check(Node root);

if ( data == null ) {
 // do something
} else {
 // do something
}

On the other hand, if check() is declared to return int, it can never be null and the whole if-else block is then superfluous.

int data = check(Node root);

// do something

Autoboxing problems doesn't apply here as well when check() is declared to return int. If it had returned Integer, then you may risk NullPointerException when assigning it to an int instead of Integer. Assigning it as an Integer and using the if-else block would then indeed have been mandatory.

To learn more about autoboxing, check this Sun guide.

No. Only object references can be null, not primitives.

I'm no expert, but I do believe that the null equivalent for an int is 0.

For example, if you make an int[], each slot contains 0 as opposed to null, unless you set it to something else.

In some situations, this may be of use.

Since you ask for another way to accomplish your goal, I suggest you use a wrapper class:

new Integer(null);

instead of declaring as int i declare it as Integer i then we can do i=null;

Integer i;
i=null;

Integer object would be best. If you must use primitives you can use a value that does not exist in your use case. Negative height does not exist for people, so

public int getHeight(String name){
    if(map.containsKey(name)){
        return map.get(name);
    }else{
        return -1;
    }
}

As @Glen mentioned in a comment, you basically have two ways around this:

• use an "out of bound" value. For instance, if "data" can never be negative in normal use, return a negative value to indicate it's invalid.
• Use an Integer. Just make sure the "check" method returns an Integer, and you assign it to an Integer not an int. Because if an "int" gets involved along the way, the automatic boxing and unboxing can cause problems.

No, but int[] can be.

int[] hayhay = null; //: allowed (int[] is reference type)
int   hayno  = null; //: error   (int   is primitive type)
                     //: Message: incompatible types: 
                     //: <null> cannot be converted to int

Along with all above answer i would like to add this point too.

For primitive types,we have fixed memory size i.e for int we have 4 bytes and char we have 2 bytes. And null is used only for objects because there memory size is not fixed.

So by default we have,

   int a=0;

and not

   int a=null;

Same with other primitive types and hence null is only used for objects and not for primitive types.

An int is not null, it may be 0 if not initialized. If you want an integer to be able to be null, you need to use Integer instead of int . primitives don't have null value. default have for an int is 0.

Data Type / Default Value (for fields)

int ------------------ 0

long ---------------- 0L

float ---------------- 0.0f

double ------------- 0.0d

char --------------- '\u0000'

String --------------- null

boolean ------------ false

A great way to find out:

public static void main(String args[]) {
    int i = null;
}

Try to compile.

Any Primitive data type like int,boolean, or float etc can't store the null(lateral),since java has provided Wrapper class for storing the same like int to Integer,boolean to Boolean.

Eg: Integer i=null;

In Java, int is a primitive type and it is not considered an object. Only objects can have a null value. So the answer to your question is no, it can't be null. But it's not that simple, because there are objects that represent most primitive types.

The class Integer represents an int value, but it can hold a null value. Depending on your check method, you could be returning an int or an Integer.

This behavior is different from some more purely object oriented languages like Ruby, where even "primitive" things like ints are considered objects.

Check for null in your check() method and return an invalid value such as -1 or zero if null. Then the check would be for that value rather than passing the null along. This would be a normal thing to do in old time 'C'.