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Help in generics....

Nitish Bangera
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Joined: Jul 15, 2009
Posts: 537



This question is from SCJP 6 khalid mughal. The answer to this question is b and c.

well i understand that car can be added but how is sedan put because it says car or super of car(Vehicle or Object).....

Also please explain the other <? extends Car> also.


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Muhammad Khojaye
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Joined: Apr 12, 2009
Posts: 449

For Garage<? super Car> we can pass either Car or any subclass of the Car to the add() method, but we cannot pass a super class of Car. Also see this


http://muhammadkhojaye.blogspot.com/
Nitish Bangera
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Joined: Jul 15, 2009
Posts: 537

I guess i confused myself..... This example is like Garage<? super Car> g = new Garage<Car/SUpertype>();

I confused it to to the example given in K&B page 619 where they pass List<Animal> a. reference "a" is passed to a method(List<? super Dog> e) But still a little confusion..... why does it allow as we pass a list<Animal> to a method(list<? super Dog>.)

with raw type object references its not possible as the compiler has no idea which instance it points to or which super type it is going to point to.

I guess i understand a little bit over the problem here..... It is because the V in garage cannot be determined at compile time where as in animal and dog it was determined at compile time that the super of dog is animal.
Nitish Bangera
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Joined: Jul 15, 2009
Posts: 537

I really confused myself big time...but i am clear now. When we pass a List<animal> a to a method(List<? super Dog> e)..here we are dealing with references and the compiler knows it. Well if we are talking about List<? super Dog> a = something. compiler really doesn't know what the something object will be that's why we cannot add anything into the list.
 
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subject: Help in generics....