[Java] Instanceof

 Instanceof

- instanceof operator is used to test whether the object is an instance of the specified type

- It is also known as type comparison operator

- It returns either true or false

1. Example

public class Test{ public static void main(String[]args){ Test a = new Test(); System.out.println(a instanceof Test); } }

- true

2. instanceof in java with a variable that have null value

public class Test{ public static void main(String[]args){ Test a = null; System.out.println(a instanceof Test); } }  

- false

3. Downcasting with java instanceof operator

1) Downcasting

- When subclass type refers to the object of Parent class, it is known as downcasting

Dog d = new AnImal(); //Compilation error  

Dog d = (Dog) new Animal() // ClassCastException  

2) Possibility of downcasting with instanceof

package statics; class Animal{ } class Dog extends Animal{ static void method(Animal a){ if(a instanceof Dog){ Dog d = (Dog)a;//down } } } public class Test{ public static void main(String[]args){ Animal a = new Dog(); Dog.method(a); } }  

3) Downcasting without the use of instanceof

class Animal{ } class Dog extends Animal{ static void method(Animal a){ Dog d = (Dog)a;//down } } public class Test{ public static void main(String[]args){ Animal a = new Dog(); Dog.method(a); } }