The instanceof operator in java is mainly used to check whether an object is an instance of a specific class or not. It is also known as comparison operator because it compares the instance with type.
instanceof is a binary operator, it returns either true or false.
- The instanceof operator provides a way to find type information of an object at runtime.
- It is a boolean operator and returns either true or false depending upon whether object is an instance of given class or not.
- instanceof operator is also used for type casting object at runtime.
- instanceof operator will return false if we apply instanceof operator to null.
- All java classes inherits from Object class. So, instances of all the classes are also an instance of the Object class.
- instanceof returning false for null object.
Syntax of instanceof operator
objectName instanceOf className;
If objectName is an instance of className, the operator returns true. Otherwise, it returns false.
Example java program for instanceof operator
class Shirt {
}
public class InstanceofOperator {
public static void main(String[] args) {
// Basic data types
String tcc = "TechCrashCourse";
// User defined object
Shirt shirt = new Shirt();
// Check if tcc is an instance of String
boolean isString = tcc instanceof String;
System.out.println("isString: " + isString);
// Check if shirt is an instance of Shirt
boolean isShirt = shirt instanceof Shirt;
System.out.println("isShirt: " + isShirt);
}
}
Output
isString: true isShirt: true
In the above program, we have created a String variable named tcc and an object shirt of the Shirt class.
We are using instanceof operator to check whether tcc is an instance of String or not and whether shirt is an instance of class Shirt or not. In both cases instanceof operator returned true.
Java instanceof operator during inheritance
We can use instanceof operator in java to check if an object is an instance of child class or parent class.
- An object of child type is also an instance of parent class.
- An object of parent class type is not an instance of child class.
// Parent class
class Animal {
}
// Child class
class Tiger extends Animal {
}
public class InstanceofOperator {
public static void main(String[] args) {
// Create object of parent class
Animal a = new Animal();
// Create object of child class
Tiger t = new Tiger();
// Check if t is an instance of Tiger(child)
System.out.println(t instanceof Tiger); // true
// Check if t is an instance of Animal(parent)
System.out.println(t instanceof Animal); // true
// Check if a is an instance of Tiger(child)
System.out.println(a instanceof Tiger); // false
// Check if a is an instance of Animal(parent)
System.out.println(a instanceof Animal); // true
}
}
Output
true true false true
In the above program, we have created a child class Tiger which inherits from the parent class Animal. We have created an object of Animal and Tiger class named "a" and "t" respectively.
Inside main method, we are using instanceof operator to check that a child class instance(t) is also an instance of parent class whereas an instance of parent class(a) is not an instance of child class.
Java instanceof operator in interface
The instanceof operator in java can also be used to check whether an object of a class is also an instance of the interface implemented by the class.
// Interface
interface Runner {
void run();
}
class Tiger implements Runner {
public void run() {
System.out.println("Tiger is running.");
}
}
public class InstanceofOperator {
public static void main(String[] args) {
// Create object of Tiger class
Tiger t = new Tiger();
// Check if t is an instance of Tiger
System.out.println(t instanceof Tiger);
// Check if t is an instance of Runner
System.out.println(t instanceof Runner);
t.run();
}
}
Output
true true Tiger is running.
In the above program, the Tiger class implements Runner interface. Object t is an instance of Tiger class and instanceof operator checks that object t is also an instance of interface Runner.