OOPS in JAVA 18

 OOPS in JAVA 18

instanceof Operator

The java instanceof operator is used to test whether the object is an instance of the specified type (class or subclass or interface).

The instanceof in java is also known as type comparison operator because it compares the instance with type. instanceof operator return boolean value, either true or false.

Example

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

Example:

class Animal{}  
class Dog1 extends Animal{//Dog inherits Animal  
  
 public static void main(String args[]){  
 Dog1 d=new Dog1();  
 System.out.println(d instanceof Animal);//true  
 }  
}  
Output: true

Downcasting with java instanceof operator

When Subclass type refers to the object of Parent class, it is known as downcasting. If we perform it directly, compiler gives Compilation error.

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

If you perform it by typecasting, ClassCastException is thrown at runtime.

Dog d=(Dog)new Animal();
//Compiles successfully but ClassCastException is thrown at runtime.

But if we use instanceof operator, downcasting is possible 

Example : Downcasting with instanceof

class Animal {

 }  
  
class Dog extends Animal {  
  static void method(Animal a) {  
    if(a instanceof Dog){  
       Dog d=(Dog)a;//downcasting  
       System.out.println("ok downcasting performed");  
    }  
  }  
   
  public static void main (String [] args) {  
    Animal a=new Dog();  
    Dog.method(a);  
  }  
    
 }  
Output: ok downcasting performed