what is the difference in E and T?

[Raju Champaklal]

am really confused in this part that is given in k&b....E is an element and T is a type that is not a collection? can anyone explain this to me?

[Ankit Garg]

Using E to represent elements and T for type is just a convention. You are not forced to follow it...

[Phungsuk Wangdu]

well you can use any other identifier if you wish to in place of E & T

[Raju Champaklal]

and why cant we use this?

 
class Animal{}
public class AnimalHolder<? extends Animal> {

}   

[Henry Wong]

Raju Champaklal wrote:and why cant we use this?

Assuming that it was allowed, what is it supposed to do?


Or to ask it another way, wildcards are used to declare references so that it can point to generic objects of various different type. For the actual generic object, what is supposed to happen? What is a wildcard generic object, assuming there is such a thing, supposed to do?

Henry

[Raju Champaklal]

just what T did before...replace all T with whatever came in....

[Henry Wong]

Raju Champaklal wrote:just what T did before...replace all T with whatever came in....

Yea, so what does replacing all "?" with whatever came in supposed to do? It isn't exactly behaving as a wildcard. You are asking for the "?" to be a valid type?

Henry

[Raju Champaklal]

well doesnt ? mean accept anything that comes inside...and T means replace all T with the thing that comes in....

[Henry Wong]

Raju Champaklal wrote:well doesnt ? mean accept anything that comes inside...

No. A wildcard is used to declare a reference to a generic object, where the type T is not known.

Henry

[Raju Champaklal]

oh yaa....thanks for the clear definition of ? and what about T ? T is not known...means...even ? means doesnt know ...right?

[Raju Champaklal]

the book says that E/T is a placeholder of the type you pass in...means ? cant be used in such a case....now its clear