Questions about Polymorphism

Code:

---

public class food{
  void eat(){
    System.out.println("this food is great");
  }

}

public class tuna extends food{
  void eat(){
    System.out.println("tuna is great");
  }

}

*********************************************

public class apple{
  public static void main(String[] args){
     
    food fo = new food();   
    food ft = new tuna();   
   
    fo.eat();
    ft.eat();
   
    }
}

---

According to the following code:
tuna ta = new tuna();
food ft = new tuna();

1) what is the difference between the object "ta" and "ft"?
2) what is the pros?
3) when using the code "tuna ta = new tuna();" and execute "ta.eat()",
it also produce the same result of "food ft = new tuna();",
then why "food ft = new tuna();" is introduced by Polymorphism?

I am a bit confuse on invoking the Polymorphism.
Hope anyone can help

Thanks

read about benefits of polymorphism. you will get answer........