Generic method problem

[Mohit Jain]

Hi Ranchers

What exactly does the following method body trying to declare??

public <T> List<T> meth(List<?> l)
{
return new arrayList<String>();
}

It gives compiler error, but I couldnt understand how this works.
Any help would be greatly appreciated.

[Mohit Jain]

I would appreciate if somebody could provide an explanation for this.

[Balamurugan Muthiah]

I expect the method declaration to be

public List<T> meth(List<T> l)
{
return new ArrayList<T>();
}

If that is the case, it should be implemented something like this
public List <String> meth (List <String> l)
{
return new ArrayList <String>();
}

Read generics, you will get hold of this.

[nico dotti]

Disclaimer: I'm still trying to get the generics concepts down so please cross reference my answer LOL

public <T> List<T> meth(List<?> l)
{
return new arrayList<String>();
}

If you had to keep the last line returning new arrayList<String> then you're return type generic in the method's signature should reflect that:

public List<String> meth...

and I think (not sure) you can say:

public List<? super String> meth...

which would actually allow you the option to return a list of type Objects or Strings.

I don't see why you couldn't keep the paramter list as List<?> which will allow you to pass in any type of List, especially if you're not returning that exact same List. So if the caller passed a list of type parameter<Animal> you could still return a different List<String> that was created within the method body.

Am I right bartenders? This is an area that I'm trying to get down myself :roll: