Generics

[vibhas karn]

Hi every body Its Vibhas once again. I am geting a doubt that why does this set of code is not working if i use ArrayList instead of List in the following code i have commented that part by >>>??? Question please have a look on that and expalin me with reason .. Here is the code

import java.util.*;
 
class Animal
{
}
 
class Dog extends Animal
{
String name;
 
Dog()
{
}
Dog(String n)
{
name = n;
}
 
public String toString()
{
return name;
 
}
 
}
 
class Cat extends Animal
{
String name;
 
Cat()
{
 
}
Cat(String n)
{
name = n;
}
 
public String toString()
{
return name;
 
}
}
 
public class AnimalDoctorGenric2
{
public static void main(String[] args)
{
 
List<Animal> mylist = new ArrayList<Animal>();
 
Dog d = new Dog();
Cat c = new Cat();
Animal a = new Animal();
mylist.add(new Cat("Black"));
mylist.add(new Dog("Doverman"));
 
for(Object o : mylist)
System.out.println(o);
 
AnimalDoctorGenric2 ad = new AnimalDoctorGenric2();
//ad.calldoctor(d);
  ad.calldoctor(mylist);
//ad.calldoctor(c);


}
        //>>>??? Question
public void calldoctor(List<Animal> animal)//Instead of List if i use
{
//ArrayList its giving me
//compiletime error
//eventhough i am passing Animal
//type reference....??
animal.add(new Dog("Germanshephered"));
}
}

[edit]Add code tags, and removed some excess whitespace. CR[/edit]
[ September 19, 2008: Message edited by: Campbell Ritchie ]

[Vijitha Kumara]

vibhas karn:

public void calldoctor(List<Animal> animal)//Instead of List if i use
{ //ArrayList its giving me
//compiletime error

If you want this method's parameter to be ArrayList<Animal> then you should call that method passing ArrayList<Animal> to it. But you call that method from

 List<Animal> mylist = new ArrayList<Animal>();
 .....
 ad.calldoctor(mylist);

Reference Type is List. So you cannot assign List type in to collection originally declared as ArrayList, reverse is possible.

[Thiago Sanchez]

public class AnimalDoctorGenric2
{
public static void main(String[] args)
{

List<Animal> mylist = new ArrayList<Animal>(); mylist is not an ArrayList, but a List. The JVM knows that an ArrayList is a List but not all List's are ArrayLists so you can do List<anyList> yourList = new ArrayList<anArrayList> but you can`t do ArrayList<anArrayList> youArrayList = new List<yourList>...

so if you need your List to came an ArrayList again try that:

ArrayList<Animal> anotherList;

anotherList = (ArrayList)myList;



Dog d = new Dog();
Cat c = new Cat();
Animal a = new Animal();
mylist.add(new Cat("Black"));
mylist.add(new Dog("Doverman"));

for(Object o : mylist)
System.out.println(o);

AnimalDoctorGenric2 ad = new AnimalDoctorGenric2();
//ad.calldoctor(d);

or try it
ad.calldoctor((ArrayList)mylist);
//ad.calldoctor(c);


}
//>>>??? Question
public void calldoctor(List<Animal> animal)//Instead of List if i use
{ //ArrayList its giving me
//compiletime error
//eventhough i am passing Animal
//type reference....??
animal.add(new Dog("Germanshephered"));


}
}

Sometimes programming means

[Thiago Sanchez]

:shocked: I forget A DETAIL :shocked:

ad.calldoctor((ArrayList<Animal>) mylist);
//ad.calldoctor(c);


}
//>>>??? Question
public void calldoctor(ArrayList<Animal> animal)//Instead of List if i use
{ //ArrayList its giving me
//compiletime error
//eventhough i am passing Animal
//type reference....??
animal.add(new Dog("Germanshephered"));


}
}
:shocked:
[edit]Disable smilies. CR[/edit]
[ September 19, 2008: Message edited by: Campbell Ritchie ]

[Campbell Ritchie]

Your code is really difficult to read because you have too much whitespace. That might be caused by your text editor; are you using NotePad? If so, don't, but look for Notepad2 or Notepad++ which are much better tools for programming. They will also help with indentation, matching {} etc.

I can't see what the problem is; I copied and pasted your code and it ran first time. What errors are you actually getting?
The commented-out lines appear to call a method on the AnimalDoctor class which takes Dog or Animal as a parameter, but you have no such method. That might be the cause of your problem, which has nothing whatsoever to do with generics.

[vibhas karn]

Sorry Ritche i got my mistake .... thanks

[Campbell Ritchie]

You're welcome ( ) but please tell us how you sorted it out.