How to check if an int is a null

Question

I have an object called Person   it has several attributes in it   int id  String name    i set a person object like Person p   new Person 1  Joe      1   I need to check if the object is not null  Is the following expression correct   if  person    null      Or   if person equals null     2   I need to know if the ID contains an Int   if person getId    null       But  java doesn t allow it  How can i do this check

User · Answer

1   I need to check if the object is not null  Is the following expression correct  if  person    null      YES  This is how you check if object is null   2   I need to know if the ID contains an Int  if person getId    null     NO Since id is defined as primitive int  it will be default initialized with 0 and it will never be null  There is no need to check primitive types  if they are null  They will never be null  If you want  you can compare against the default value 0 as if person getId    0

User · Answer

primitives dont have null value  default have for an int is 0    if person getId    0      Default values for primitives in java   Data Type   Default Value  for fields   byte                0 short               0 int                 0 long            0L float           0 0f double          0 0d char              u0000  boolean         false   Objects have null as default value   String  or any object --- null     1   I need to check if the object is not null  Is the following expression correct    if  person    null       the above piece of code checks if person is null  you need to do  if  person    null      checks if person is not null     and  if person equals null     The above code would throw NullPointerException when person is null

User · Answer

You have to access to your class atributes   To access to it atributes  you have to do   person id person name   where      person   is an instance of your class Person   This can be done if the attibutes can be accessed  if not  you must use setters and getters

User · Answer

A primitive int cannot be null  If you need null  use Integer instead

User · Answer

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   Integer id  String name   public Integer getId     return id      Besides the statement if person equals null   can t be true  because if person is null  then a NullPointerException will be thrown  So the correct expression is if  person    null

User · Answer

You can use   if  person    null    String valueOf person getId      null      in addition to regular approach   person getId      0

User · Answer

In Java there isn t Null values for primitive Data types  If you need to check Null use Integer Class instead of primitive type  You don t need to worry about data type difference  Java converts int primitive type data to Integer   When concerning about the memory Integer takes more memory than int  But the difference of memory allocation  nothing to be considered    In this case you must use Inter instead of int  Try below snippet and see example for more info   Integer id  String name     Refer this example     Integer val   0       if  val    null   System out println  value is not null           Also you can assign Null as below   val   null

[java] How to check if an int is a null

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