instanceof Keyword in Java (original) (raw)
Last Updated : 06 Jul, 2023
In Java, instanceof is a keyword used for checking if a reference variable contains a given type of object reference or not. Following is a Java program to show different behaviors of instanceof. Henceforth it is known as a comparison operator where the **instance is getting compared to **type returning boolean true or false as in Java we do not have 0 and 1 boolean return types.
**Example of the Java instanceof Keyword
Java
import java.io.*;
class GFG {
`` public static void main(String[] args)
`` {
`` GFG object = new GFG();
`` System.out.println(object instanceof GFG);
`` }
}
Examples of Java instaceof keyword
Here are all the examples of instanceof keywords with their respective cases:
1. Here we will be creating sample classes with a parent-child relationship.
Java
class Parent {
}
class Child extends Parent {
}
class GFG {
`` public static void main(String[] args)
`` {
`` Child cobj = new Child();
`` if (cobj instanceof Child)
`` System.out.println( "cobj is instance of Child" );
`` else
`` System.out.println(
`` "cobj is NOT instance of Child" );
`` if (cobj instanceof Parent)
`` System.out.println(
`` "cobj is instance of Parent" );
`` else
`` System.out.println(
`` "cobj is NOT instance of Parent" );
`` if (cobj instanceof Object)
`` System.out.println(
`` "cobj is instance of Object" );
`` else
`` System.out.println(
`` "cobj is NOT instance of Object" );
`` }
}
Output
cobj is instance of Child cobj is instance of Parent cobj is instance of Object
2. instanceof returning false for null
Java
class Test {
}
class Main {
`` public static void main(String[] args)
`` {
`` Test tobj = null ;
`` if (tobj instanceof Test)
`` System.out.println( "tobj is instance of Test" );
`` else
`` System.out.println(
`` "tobj is NOT instance of Test" );
`` }
}
Output
tobj is NOT instance of Test
3. Parent object is not an instance of Child
Java
class Parent {
}
class Child extends Parent {
}
class Test {
`` public static void main(String[] args)
`` {
`` Parent pobj = new Parent();
`` if (pobj instanceof Child)
`` System.out.println( "pobj is instance of Child" );
`` else
`` System.out.println(
`` "pobj is NOT instance of Child" );
`` }
}
Output
pobj is NOT instance of Child
4. Parent reference referring to a Child is an instance of a Child
Java
class Parent {
}
class Child extends Parent {
}
class Test {
`` public static void main(String[] args)
`` {
`` Parent cobj = new Child();
`` if (cobj instanceof Child)
`` System.out.println( "cobj is instance of Child" );
`` else
`` System.out.println(
`` "cobj is NOT instance of Child" );
`` }
}
Output
cobj is instance of Child
**Application of Java instanceof keyword
We have seen here that a parent class data member is accessed when a reference of parent type refers to a child object. We can access child data members using typecasting.
**Syntax
((child_class_name) Parent_Reference_variable).func.name()
When we do typecasting, it is always a good idea to check if the typecasting is valid or not. instanceof helps us here. We can always first check for validity using instanceof, then do typecasting.
**Example
Java
class Parent {
`` int value = 1000 ;
}
class Child extends Parent {
`` int value = 10 ;
}
class Test {
`` public static void main(String[] args)
`` {
`` Parent cobj = new Child();
`` Parent par = cobj;
`` if (par instanceof Child) {
`` System.out.println(
`` "Value accessed through "
`` + "parent reference with typecasting is "
`` + ((Child)par).value);
`` }
`` }
}
Output
Value accessed through parent reference with typecasting is 10