How to check if an int is a null

Question

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)

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.

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

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){}.