Reason for CLASS casting?

Question

The discussions below seem to focus of casting of data types, but did not mention the rationale for casting of classes.

Like in the example,
Animal a = new cat();

if I was meant to create an object of the superclass, I’d use
Animal a = new Animal();
if I was meant to create an object of the subclass, cat (and ask it to make sound), I’d use
Cat a = new Cat();
a.makeSound();

Then, what is the point of writing
Animal a = new cat(); (upcasting)
OR
Animal a = new Animal();
((cat).a).makeSound(); (downcasting)?

I understand how casting works syntax-wise. I understand why do we cast datatypes. But I have no idea why we cast classes.

Any real-life example or source-code based elaboration?

Answer 1

Well this is one of the OOP concept.

Ex:

class Car {
public String getCompany(){
return null;
}
}

class Corola extends Car {
public String getCompany(){
return "Toyota";
}
}

class City extends Car {
public String getCompany(){
return "Honda";
}
}

class Test {

public static void main (String[] args){
Car c1 = new Corola ();
Car c2 = new City ();

show (c1); //Toyota
show (c2); //Honda
}

// show method accepts all classes that extend Car
public static void show (Car car){
System.out.println (car.getCompany ());
}

}

Answer 2

nice answer but I want to add 1 more thing
if class City has one more method
public int getPrice(){
return 10;
}

then we can't call this method like this
c2.getPrice();
because class Car doesn't has dis method
here we have to use downcast

((City)c2).getPrice();

Answer 3

Good example.

Answer 4

Is Sidd right?