Java instanceof Operator

The instanceof operator in Java is used to check whether an object is an instance of a particular class or not.

Its syntax is

objectName instanceOf className;

Here, if objectName is an instance of className, the operator returns true. Otherwise, it returns false.

Example: Java instanceof

class Main {

  public static void main(String[] args) {

    // create a variable of string type
    String name = "Programiz";
    
    // checks if name is instance of String
    boolean result1 = name instanceof String;
    System.out.println("name is an instance of String: " + result1);

    // create an object of Main
    Main obj = new Main();

    // checks if obj is an instance of Main
    boolean result2 = obj instanceof Main;
    System.out.println("obj is an instance of Main: " + result2);
  }
}

Output

name is an instance of String: true
obj is an instance of Main: true

In the above example, we have created a variable name of the String type and an object obj of the Main class.

Here, we have used the instanceof operator to check whether name and obj are instances of the String and Main class respectively. And, the operator returns true in both cases.

Note: In Java, String is a class rather than a primitive data type. To learn more, visit Java String.

Java instanceof during Inheritance

We can use the instanceof operator to check if objects of the subclass is also an instance of the superclass. For example,

// Java Program to check if an object of the subclass
// is also an instance of the superclass

// superclass
class Animal {
}

// subclass
class Dog extends Animal {
}

class Main {
  public static void main(String[] args) {

    // create an object of the subclass
    Dog d1 = new Dog();

    // checks if d1 is an instance of the subclass
    System.out.println(d1 instanceof Dog);        // prints true

    // checks if d1 is an instance of the superclass
    System.out.println(d1 instanceof Animal);     // prints true
  }
}

In the above example, we have created a subclass Dog that inherits from the superclass Animal. We have created an object d1 of the Dog class.

Inside the print statement, notice the expression,

d1 instanceof Animal

Here, we are using the instanceof operator to check whether d1 is also an instance of the superclass Animal.

Java instanceof in Interface

The instanceof operator is also used to check whether an object of a class is also an instance of the interface implemented by the class. For example,

// Java program to check if an object of a class is also
//  an instance of the interface implemented by the class

interface Animal {
}

class Dog implements Animal {
}

class Main {
  public static void main(String[] args) {

    // create an object of the Dog class
    Dog d1 = new Dog();

    // checks if the object of Dog
    // is also an instance of Animal
    System.out.println(d1 instanceof Animal);  // returns true
  }
}

In the above example, the Dog class implements the Animal interface. Inside the print statement, notice the expression,

d1 instanceof Animal

Here, d1 is an instance of Dog class. The instanceof operator checks if d1 is also an instance of the interface Animal.

d1 instanceof Object

Also Read:

• Java Program to Determine the class of an object