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Problem in using keyword "super" with generics

 
Ranch Hand
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class Animal{}
class Dog extends Animal{}
class Puppy extends Dog{}

public class Generic2 {
public static void main(String[] args) {
List <? super Dog>dogList = new ArrayList<Dog>(); //1
dogList.add(new Dog());
dogList.add(new Puppy()); //2
dogList.add(new Animal()); //3
}
}

<? super Dog> (at line //1 ) this says that List reference dogList can accept anything that is either a Dog or a superclass of Dog.
Then why does'nt it give an error when i am trying to add an object of class Puppy to it ? line marked //2
Also why does it give me an error when i am trying to add an object of class Animal to it ? line marked //3

Pl explain
 
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Hi Prasad,

List <? super Dog> dogList = new ArrayList<Dog>();

Means dogList can be added "Any Object which IS-A Dog".

1) Puppy IS-A Dog // Correct
2) Animal IS-A Dog // Need Not be.

Hope you got it.
 
Greenhorn
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Hi all, first comment here in javaranch =).

Well, i have a dude in generics and wilcards.

The next is not allowed=
List<Animal> list = new ArrayList<Dog>()

Of course, polymorphism with generics get us to a nice compiler error.

But with wilcards, isnt it the same?

List<? extends Animal> list = new ArrayList<Dog>();
is ok, i think...

But with return types, is this ok?

public List<? extends Animal> maybeGetDogs(List<Animal>
{
...
}

List<Dog> dog = maybeGetDogs(animals);

And about the code wich wrote our friend in the first post, what does it throw? I think compiler error, because in runtime there arent generics...

-A pleasure write here.Thanks for all, and sorry for my english -spanish, lot of sun and beach and bulls, but bad english.
 
Prasad Shindikar
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hi Srinivasan,

i got it mate. thanks a lot
 
Srinivasan thoyyeti
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Hi Antonio,

you are correct.
Please find the reply relevant to your query.
https://coderanch.com/t/262080/java-programmer-SCJP/certification/Generic

Lets Program Better.
 
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