I saw an example of Java Generic in the above link. It is not using this type of declaration. I want to create a LL. If I want to declare them how should I declare them? Why its accepting them in the "GenericsType" class? Somebody please guide me.
It's accepting T1 and T2 for the members of GenericsType, because you've declared those type variables in the first line when you declared GenericsType. Your BuiltInLLApp has no such declarations and they also wouldn't do you any good because you would be using them in the static main() method. Generic type parameters declared at the start of a class are only for instance members.
What you probably want to do is declare your head, tail and newNode variables in such a way that they use concrete types and not type parameters. The second code snippet under the heading "2. Java Generic Class" from the link you posted shows you how to do that with the String class.
Don't use T1 and T2 as formal type parameters (line 1, etc.). Use single letters e.g. GenericsType<T, U>. Don't call the fields id or name, because that will make you think they will have particular uses. Your users can use any type they like, so call them t and u. Try not to let the users see those field names
Your users will declare the object reference as type GenericsType<Integer, Double> or GenericsType<List<Foo>>, Set<Bar>> or something else.
Don't use _ in your method names. Use mixedCase(). Pease be sure to indent your code correctly; you can cause yourself no end of confusion wth badly indented code.