Returning null in a method whose signature says return int

Question

public int pollDecrementHigherKey int x                int savedKey  savedValue              if  this higherKey x     null                    return null      COMPILE-TIME ERROR                           else if  this get this higherKey x    gt  1                            savedKey   this higherKey x                   savedValue   this get this higherKey x   - 1                  this remove savedKey                   this put savedKey  savedValue                   return savedKey                            else                   savedKey   this higherKey x                   this remove savedKey                   return savedKey                            The method lies within a class that is an extension of TreeMap  if that makes any difference    Any ideas why I can t return null here

User · Answer

Do you realy want to return null   Something you can do  is maybe initialise savedkey with 0 value and return 0 as a null value  It can be more simple

User · Answer

int is a primitive data type   It is not a reference variable which can take null values   You need to change the method return type to Integer wrapper class

User · Answer

The type int is a primitive and it cannot be null  if you want to return null  mark the signature as public Integer pollDecrementHigherKey int x        x   10       if  condition            return x     This is auto-boxing  x will be automatically converted to Integer       else if  condition2            return null     Integer inherits from Object  so it s valid to return null       else           return new Integer x      Create an Integer from the int and then return                return 5     Also will be autoboxed and converted into Integer

User · Answer

Change your return type to java lang Integer   This way you can safely return null

User · Answer

int is a primitive  null is not a value that it can take on  You could change the method return type to return java lang Integer and then you can return null  and existing code that returns int will get autoboxed   Nulls are assigned only to reference types  it means the reference doesn t point to anything  Primitives are not reference types  they are values  so they are never set to null    Using the object wrapper java lang Integer as the return value means you are passing back an Object and the object reference can be null

[java] Returning null in a method whose signature says return int?

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