Arrays

[garima jain]

I wrote the following program:

 
class animal {
    public void go()
{System.out.println("animal");}
}
 
class dog extends animal{
    public void go()
{System.out.println("dog");}
}
 
class cat extends animal{
    public void go()
{System.out.println("cat");}
}
public class testarr {
public static void main(String[] args) {
        animal[] a = new dog[3];
a[0]= new animal();
a[0].go();
     }
}

In the above program, what is the array type for array a. Is it animal or dog. Please explain. I thought it would be animal and the program would run fine. However, it is giving me ArrayStoreExcpetion.

[ Jesper Young: Corrected use of code tags ]
[ November 04, 2008: Message edited by: Jesper Young ]

[victor kamat]

a's type is Animal[]. As to the rest I do not have a good answer.

[Ganeshkumar cheekati]

I think that

animal[] a = new dog[3];

you created dog array object which is referenced by animal a.

a[0]= new animal();

it is object of type dog then how can you put animal in dog?

dog is an animal but not vice-versa.

correct me if i am wrong.....

[pradeepta chopra]

hi garima,

the reason you are getting an ArrayStoreException is because you are trying to add an Animal into a Dog array.

Note:
You can add a subtype(Dog) object to an array of the supertype(Animal),not vice versa.

if you change the main method as

public static void main(String[] args) {
        animal[] a = new dog[3];
a[0]= new dog(); // [B]adding a dog to a Dog type of array which is referenced by an Animal ref variable[/B]
a[0].go();
     }

the code now compiles fine.
Hope you get the point

[pradeepta chopra]

correct Ganeshkumar

[Anoobkumar Padmanabhan]

As Ganesh explains, the program will create an array of type dog, and this array will be refenced using animal refernce. Anyway, the objects that can be stored in the array should be of type dog.

So that will throw an exception, if you try to add an animal object to the array

[garima jain]

What about this code

Parent[] p = {new Dog(), new Cat()};

Here p is of type Parent. Am i right.

[garima jain]

Sorry for the typo

It should be
animal[] p = {new dog(), new cat()};

[Ankit Garg]

animal[] p = {new dog(), new cat()};

Here p is of type animal...

[Anoobkumar Padmanabhan]

Hi

But P is just a refence of type animal right?
It is not the actula array or object.

[Ankit Garg]

p is a array reference which can store objects of type animal and it's sub types.....

[Madan Mohan]

i am still not clear on this...?

[Madan Mohan]

for example : here also we are doing the same

class Animal {
public void eat() {
System.out.println("Animal");
}
}
class Dog extends Animal {

public void eat() {
System.out.println("Dog");
}
}
class DemoClass{

public static void main(String args[]){

Animal dog = new Dog();
dog = new Animal();
dog.eat(); // <--- here

}

}
but this comiles fine...then why not in the case of array...

[Henry Wong]

You have to distinguish the array and the elements of the array. A dog array IS-A animal array, and hence, can be referred to by an animal array reference. However, it is still a dog array, that is being referred to, whose elements must be objects that IS-A dog type.

Henry