instanceof Operator in Java:
The instanceof operator is used to check whether an object is an instance of a specific class or subclass. It returns a boolean value — true if the object is of the specified type, otherwise false.
Syntax
object instanceof ClassNameUse Case
Useful when working with inheritance, polymorphism, or type checking before casting an object.
Example:
public class ShikshaSanchar {
public static void main(String[] args) {
String name = "Simran";
Integer number = 100;
System.out.println(name instanceof String); // true
System.out.println(number instanceof Integer); // true
System.out.println(name instanceof Object); // true
Object obj = "Hello";
System.out.println(obj instanceof String); // true
System.out.println(obj instanceof Integer); // false
}
}Output:
true
true
true
true
false
Explanation:
- name instanceof String → true, because name is a String.
- number instanceof Integer → true, since number is an Integer.
- name instanceof Object → true, because all classes in Java inherit from Object.
- obj instanceof String → true, as obj refers to a String.
- obj instanceof Integer → false, obj is not an Integer.
Example: null Check
public class ShikshaSanchar {
public static void main(String[] args) {
String str = null;
System.out.println("Is str an instance of String? " + (str instanceof String));
}
}Output:
Is str an instance of String? false
Explanation:
- str is declared as a String but currently holds null.
- instanceof checks whether str refers to a valid object of type String.
- Since null doesn’t point to any object, str instanceof String → false.
Summary:
- instanceof checks if an object belongs to a class or subclass.
- Returns true if object is compatible with the class type.
- Useful in type checking and avoiding ClassCastException.
- Works with interfaces too: obj instanceof InterfaceName.
- null instanceof Type always returns false, because null doesn't refer to any actual object in memory.