Can an int be null in Java

Question

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

User · Answer

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

User · Answer

No  but int   can be   int   hayhay   null      allowed  int   is reference type  int   hayno    null      error    int   is primitive type                           Message  incompatible types                             lt null gt  cannot be converted to int

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int can t be null  but Integer can  You need to be careful when unboxing null Integers since this can cause a lot of confusion and head scratching    e g  this   int a   object getA       getA returns a null Integer   will give you a NullPointerException  despite object not being null   To follow up on your question  if you want to indicate the absence of a value  I would investigate java util Optional lt Integer gt

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A great way to find out   public static void main String args          int i   null      Try to compile

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Since you ask for another way to accomplish your goal  I suggest you use a wrapper class   new Integer null

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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

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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

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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

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

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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

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No  Only object references can be null  not primitives

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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

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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

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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

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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

[java] Can an int be null in Java?

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