Reference Variable Casting?

[Hennry Smith]

class Animal {
void makeNoise() {System.out.println("generic noise"); }
}
class Dog extends Animal {
void makeNoise() {System.out.println("bark"); }
void playDead() { System.out.println("roll over"); }
}
class CastTest2 {
public static void main(String [] args) {
Animal [] a = {new Animal(), new Dog(), new Animal() };
for(Animal animal : a) {
animal.makeNoise();
if(animal instanceof Dog) {
animal.playDead(); // try to do a Dog behavior ?
}
}
}
}

When we try to compile this code, the compiler says something like this:
cannot find symbol
The compiler is saying, "Hey, class Animal doesn't have a playDead() method".
Let's modify the if code block:
if(animal instanceof Dog) {
Dog d = (Dog) animal; // casting the ref. var.
d.playDead();
}

Please explain i am not able to understand this concept...???

[Abhinav Yadav]

This is happening because the class Animal is a super class and it has only one method and that is

makeNoise( )

and Dog is its subclass ,its simple to explain that why compiler shows error it is because when object of Dog is created in

Animal [] a = {new Animal(), new Dog(), new Animal() }; 

it is stored in reference of type Animal
and in case of function overriding it depends upon the reference variable used to call the function and not upon the object it is storing.
Since there is no function named playDead() in the class Animal thus error is shown.

[Vidya sumanasekara]

This happens because of the overriding...

In the supper class Animal -> void makeNoise()

In the sub class Dog-> void makeNoise()//overriden method & playDead()// this is unique for this class

Then you have assining a dog instance to the Animal reference ( in the loop)

In that case compiler check
Animal animal=new Dog();
first reference type (Animal) where there is playDead() method and runtime check the instance type. ok..
In your case there is no any method playDead() in Animal class..so compiler gives an error..

Hennry Smith wrote:

class Animal {
void makeNoise() {System.out.println("generic noise"); }
}
class Dog extends Animal {
void makeNoise() {System.out.println("bark"); }
void playDead() { System.out.println("roll over"); }
}
class CastTest2 {
public static void main(String [] args) {
Animal [] a = {new Animal(), new Dog(), new Animal() };
for(Animal animal : a) {
animal.makeNoise();
if(animal instanceof Dog) {
animal.playDead(); // try to do a Dog behavior ?
}
}
}
}

When we try to compile this code, the compiler says something like this:
cannot find symbol
The compiler is saying, "Hey, class Animal doesn't have a playDead() method".
Let's modify the if code block:
if(animal instanceof Dog) {
Dog d = (Dog) animal; // casting the ref. var.
d.playDead();
}

Please explain i am not able to understand this concept...???

[Leon Omk]

Animal [] a = {new Animal(), new Dog(), new Animal() };  

1. This statement says: I don't care what array of animals you give me as long as they are "Animal". Because I just want to use them as "Animal", if they have special gifts , then save them for their girl friends.

class Animal {  
void makeNoise() {System.out.println("generic noise"); }  
}

2. And when I say "Animal", I mean they can makeNoise().

animal.playDead();

3. When I write this, Java compiler complains: hey, boss, you either make "Animal" can playDead(), or accept the reality by correcting this statement.