//run time polymorphism 
class parent{
    public void display(){
        System.out.println("this is a parent class");
    }
}
class child extends parent{
    public void display(){
        System.out.println("this is a child class");
    }
}
public class Main{
    public static void main(String[] args){
        parent obj=new parent();
        obj.display();
        // now we want to see display() of child class too... 
        parent obj1=new child();
        obj1.display();
    }
}