java instanceof

An instanceof in Java is a comparison operator which, given an object instance, 
checks whether that instance is of a specified type (class/sub-class/interface) 
or not. Just like other comparison operators, it returns true or false.

Comparing any object instance with a null type through instanceof operator 
returns a false.
  
Instanceof operator is used to test the object is of which type.

Syntax : <reference expression> instanceof <destination type>
Instanceof returns true if reference expression is subtype of destination type.
Instanceof returns false if reference expression is null.

public class MyClass {
  public static void main(String[] args) {
    String myStr = "Hello planet earth, you are a great planet.";
    System.out.println(myStr.lastIndexOf("planet"));
  }
}

The instanceof operator tests to see if the prototype property of a constructor 
appears anywhere in the prototype chain of an object. The return value is a 
boolean value.
For example :-

function Car(make, model, year) {
  this.make = make;
  this.model = model;
  this.year = year;
}
const auto = new Car('Honda', 'Accord', 1998);

console.log(auto instanceof Car);
// expected output: true

console.log(auto instanceof Object);
// expected output: true

(object) instanceof (type)