Java instanceof Operator

The instanceof operator is used in Java to test if an object is an instance of a particular class or one of its subclasses. The operator returns a boolean value (true or false) based on whether or not the object is an instance of the specified class or any of its subclasses.

Syntax

The instanceof operator has the following syntax:

object instanceof class

where object is the object to be tested and class is the class or interface being tested against.

Example

Here is an example that demonstrates the use of the instanceof operator:

public class Example {
    public static void main(String[] args) {
        Object obj1 = new String("Hello");
        Object obj2 = new Integer(10);

        System.out.println(obj1 instanceof String); // true
        System.out.println(obj1 instanceof Object); // true
        System.out.println(obj2 instanceof Integer); // true
        System.out.println(obj2 instanceof Number); // true
        System.out.println(obj2 instanceof Object); // true
        System.out.println(obj1 instanceof Integer); // false
        System.out.println(obj2 instanceof String); // false
    }
}

In this example, we create two objects obj1 and obj2 of type String and Integer, respectively. We then test these objects using the instanceof operator.

Output

The output of the above code will be:

true
true
true
true
true
false
false

Explanation

In the first System.out.println() statement, we test if obj1 is an instance of the String class. Since it is, the result is true.

In the second System.out.println() statement, we test if obj1 is an instance of the Object class. Since String is a subclass of Object, the result is true.

In the third to fifth System.out.println() statements, we test if obj2 is an instance of the Integer, Number, and Object classes, respectively. Since Integer extends Number which extends Object, all three tests result in true.

In the sixth and seventh System.out.println() statements, we test if obj1 is an instance of the Integer class and if obj2 is an instance of the String class, respectively. Since neither of these objects are of the specified class or its subclass, both tests result in false.

Use

The instanceof operator is often used in Java to ensure the proper handling of objects in a program. It is used, for example, in an if statement to check if an object is of a particular class before casting it to that class. This helps to prevent runtime errors that occur when a cast is attempted on an object of the wrong class.

Important Points

• The instanceof operator is used to test if an object is an instance of a particular class or one of its subclasses.
• The operator returns a boolean value (true or false) based on the object's class or one of its subclasses.
• The instanceof operator is often used to ensure the proper handling of objects in a program.

Summary

The instanceof operator is a useful tool in Java that allows for the testing of an object's class or one of its subclasses. It is used to ensure proper handling of objects in a program and to prevent runtime errors that occur when casts are attempted on objects of the wrong class.