How to check if a double is null

Question

I m querying a database and some of the results I m getting are null  I m setting these values to a variable with a datatype of double  Let s call the variable  results   So I tried setting up an if statement to see it equals Null which of course didn t work  Here is the code I have for that if statement   if  results    null         results   0      The error I get with this code is   The operator    is undefined for the argument type s  double  null  Is there a better way to determine if it s null

User · Answer

How are you getting the value of  results   Are you getting it via ResultSet getDouble    In that case  you can check ResultSet wasNull

User · Answer

To say that something  is null  means that it is a reference to the null value   Primitives  int  double  float  etc  are by definition not reference types  so they cannot have null values   You will need to find out what your database wrapper will do in this case

User · Answer

Firstly  a Java double cannot be null  and cannot be compared with a Java null    The double type is a primitive  non-reference  type and primitive types cannot be null    Next  if you call ResultSet getDouble       that returns a double not a Double  the documented behaviour is that a NULL  from the database  will be returned as zero    See javadoc linked above    That is no help if zero is a legitimate value for that column   So your options are    use ResultSet wasNull   to test for a  database  NULL     immediately after the getDouble      call  or use ResultSet getObject       and type cast the result to Double    The getObject method will deliver the value as a Double  assuming that the column type is double   and is documented to return null for a NULL    For more information  this page documents the default mappings of SQL types to Java types  and therefore what actual type you should expect getObject to deliver

User · Answer

I would recommend using a Double not a double as your type then you check against null

User · Answer

A double primitive in Java can never be null  It will be initialized to 0 0 if no value has been given for it  except when declaring a local double variable and not assigning a value  but this will produce a compile-time error    More info on default primitive values here

User · Answer

I believe Double NaN might be able to cover this  That is the only  null  value double contains

[java] How to check if a double is null?

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