Hello guys, I am wondering what does following statement mean, please
help me understand, thanks you!

First first = new Second();

The entire source code is here:

public class Main {
   public static void main(String[] args) {
       First first = new Second();        
   }
}

class First{
   void printMe(){
       System.out.println("First Hello!");
   }    
}

class Second extends First{
   void printMe(){
       System.out.println("Second Hello");
   }
}