Downcasting with instanceof Operator

Question

Downcasting is when child class refers to the object of Parent class. I tried doing it without the instanceof operator.

class Food { }  
class bread4 extends Foo         


        

Answer 1

instanceof operator provides runtime type checking. For instance, if you had a class Food and two subtypes, Bread4 and Bread5, then:

static void method(Food a) {
   Bread4 b = (Bread4) a;
   System.out.println("Downcasting performed"); 
}

calling this method like:

Food four = new Bread4();
Food five = new Bread5();
Bread4.method(four); //the cast inside is done to Bread4, therefore this would work
Bread4.method(five); //the object of type Bread5 will be cast to Bread4 -> ClassCastException

To avoid this, you use the instanceof operator

static void method(Food a) {
   if (a instanceof Bread4) {
       Bread4 b = (Bread4) a;
       System.out.println("Downcasting performed"); 
   }
}

therefore, in case you call

Bread4.method(five)

the check return false so no ClassCastException occurs.

Hope this answers your question.