Generics

[kathir vel]

Hi All,
In this following program I couldn't see the execution of Line 1 and Line 2. Anyone please clarify me?Thanks.

import java.util.*;
 
abstract class Animal {
    public abstract void checkup();
}
 
class Dog extends Animal {
    public void checkup() { // implement Dog-specific code
        System.out.println("Dog checkup");
    }
}
 
class Cat extends Animal {
    public void checkup() { // implement Cat-specific code
        System.out.println("Cat checkup");
    }
}
 
class Bird extends Animal {
    public void checkup() { // implement Bird-specific code
        System.out.println("Bird checkup");
    }
}
 
 
public class AnimalDoctorGeneric2 {
    // change the argument from Animal[] to ArrayList<Animal>
    public void checkAnimals(ArrayList< Animal> animals) {     
        animals.add(new Dog());    
        System.out.println("size is "+animals.size()); //Line1
        for(Animal a : animals) {
            System.out.println("hi ");                 //Line2
            a.checkup();
        }
    }
 
    public static void main(String[] args) {
        // make ArrayLists instead of arrays for Dog, Cat, Bird
        List< Animal> dogs = new ArrayList<Animal>();                     
        dogs.add(new Dog());
        dogs.add(new Dog());
        List<Animal> cats = new ArrayList<Animal>();
        cats.add(new Cat());
        cats.add(new Cat());
        List<Animal> birds = new ArrayList<Animal>();
        birds.add(new Bird());
        // this code is the same as the Array version
        AnimalDoctorGeneric1 doc = new AnimalDoctorGeneric1();
        // this worked when we used arrays instead of ArrayLists
        doc.checkAnimals(dogs);      
        doc.checkAnimals(cats); 
        doc.checkAnimals(birds);
        System.out.println("hi "+dogs.size()); 
    }
}

code indenting repaired by using the button, Bu
[ July 18, 2007: Message edited by: Burkhard Hassel ]

[Chandra Bhatt]

Hi Kathir,

What couldn't you see on line #1 and #2. You are passing a list to the method,
adding Dog, Cat and Bird objects to it accordingly. Inside the method, you are
adding a Dog object to every passed list and after printing its size, you
are traversing the list.
What do you see wrong there?



Thanks,

[kathir vel]

Sorry all!!.
I was using AnimalDoctorGeneric1 instead of AnimalDoctorGeneric2 .It was working fine.

[Abdullah Mamun]

Hi Kathir,
The source gives compiler error at the following lines

doc.checkAnimals(dogs);
doc.checkAnimals(cats);
doc.checkAnimals(birds);

The reason is, there is a down casting from List to ArrayList. So you have to cast explicitly.

doc.checkAnimals(( ArrayList<Animal> ) dogs);

[ July 17, 2007: Message edited by: Al Mamun ]