Java instanceof and Its Applications

instanceof operator is used to check the type of object passed. Following rules explain the usage of instanceof operator in Java.

• instanceof operator returns true for the object if checked against its class type.

• instanceof operator returns false for the object if checked against its type which is not in its hierarchy.

• instanceof operator returns true for the child object if checked against parent object type.

• instanceof operator returns true for the complete object hierarchy up to the Object class.

• instanceof operator returns false for the null value.

• instanceof operator returns false for the parent object if checked against child object type.

Following example showcases the above concepts.

Example

 Live Demo

class SuperClass {
   int value = 10;
}

class SubClass extends SuperClass {
   int value = 12;
}

public class Tester{
   public static void main(String[] args){
      SuperClass obj = new SubClass();

      //instanceof returns true for the complete Object Hierarchy
      if(obj instanceof SubClass){
         System.out.println("obj is instanceof SubClass");
      }
      if(obj instanceof SuperClass){
         System.out.println("obj is instanceof SuperClass");
      }
      if(obj instanceof Object){
         System.out.println("obj is instanceof Object");
      }

      SuperClass obj1 = null;

      //instanceof returns false for null
      if(obj1 instanceof SuperClass){
         System.out.println("null is instanceof SuperClass");
      }

      SuperClass obj2 = new SuperClass();

      //instanceof returns false for the subclass
      if(obj2 instanceof SubClass){
         System.out.println("obj2 is instanceof SubClass");
      }
      if(obj2 instanceof SuperClass){
         System.out.println("obj2 is instanceof SuperClass");
      }
   }
}

Output

obj is instanceof SubClass
obj is instanceof SuperClass
obj is instanceof Object
obj2 is instanceof SuperClass