Arrays Doubt

[aslika bahini]

Hi There,

I have a doubt in the following code.
In the line #1 animal[0]= new Cat(); throws an ArraysStoreException.
Can any of you please explain?

   import java.util.*;
 abstract class Animals {
 public void eat()
 {
  System.out.println("Inside Animals eat()");
 }
}
class Dog extends Animals
{
public void eat()
 {
  System.out.println("Inside Dog eat()");
 }

}
class Cat extends Animals
{
public void eat()
 {
  System.out.println("Inside Cat eat()");
 }

} 
 
public class AnimalsTest
{
public static void main(String args[])
{
  new AnimalsTest().go();
  
}
public void go()
{
Animals[] animal = {new Dog(),new Cat(), new Dog()};
Dog [] dogs = { new Dog(),new Dog(),new Dog()};
                takeAnimals(dogs);
        }
        public void takeAnimals(Animals[] animal)
{
animal[0]=new Cat(); //line #1

}
}

Thanks in Advance
Saritha

[Ankit Garg]

That's because Dog and Cat are siblings. You cannot add an instance of Cat into an array of Dogs.

Now you will say that the array is of Animals. But actually only the reference is an Animal array. Actually the array itself is a Dog array. Consider this code

Dog dogArr = new Dog[5];
Animal[] arr = dogArr;
arr[0]=new Cat();//ArrayStoreException
Dog dog = godArr[0];//1

Now if there was no ArrayStoreException at the line indicated, then there would be a abnormal situation at line 1. So an array can only store objects of the actual array type. You can read my blog for a detailed article. The link is in my signature...

[chander shivdasani]

It is a Classic example to why Generics came into existence

[Mohammad Khan]

// Following code might help to understand the issue


abstract class Animal {}

class Dog extends Animal {}

class Cat extends Animal {}

class Cow extends Animal {}

public class MyApp {

public static void main(String[] args) {
Animal[] animals = { new Dog(), new Cat(), new Cow() };
Dog[] dogs = { new Dog(), new Dog(), new Dog(), new Dog() };

MyApp app = new MyApp();

try {
app.doStuff(animals);
app.doStuff(dogs);
} catch (AnimalException e) {
System.out.println("Raised exception while trying to store NOT-A Dog in Dog[]");
}
}

public void doStuff(Animal[] animals) throws AnimalException {
if (animals instanceof Dog[]) {
animals[0] = new Dog();
} else {
throw new AnimalException();
}
}
}

class AnimalException extends Exception {}