The instanceof keyword checks if an object is an instance of a given class.

We can use downcasting when a class lower in the hierarchy has a method that its mother class does not. We can call this method through the child class but using the mother class object (downcasting means more or less "reverse inheritance").

public class Main {
    public static void main(String[] args) {
        Person[] p = new Person[2];
        p[0] = new Person("Liam", "Anderson");
        p[1] = new Employee("John", "Smith", 5000);

        for (Person person: p) {
            if (person instanceof Person)
                person.description();

            if (person instanceof Employee)
                ((Employee)person).work(); // downcasting
        }
    }
}

class Person {
    String name;
    String surname;
    Person(String name, String surname) {
        this.name = name;
        this.surname = surname;
    }
    void description() {
        System.out.println("I am a person!");
    }
}

class Employee extends Person {
    double salary;
    Employee(String name, String surname, double salary) {
        super(name, surname);
        this.salary = salary;
    }
    void work() {
        System.out.println("I am working!");
    }
}