Question

I just created a class like this: NameOfTheClass<Raeaeraear>. What does it means? And why can I put whatever random stuff I want?

Answer 1

That is called Generics. Generics is used to “tell” a instance of an class what kind of type it is going to work with, take f.ex a List

List<People> myPeopleList = new ArrayList<People>(); 

Here the list is parameterized. If you take a look at the List-interface source code, it is declared like this which means the interface List is generic.

public interface List<E> extends Collection<E> {
...

In your case the class NameOfTheClass would be implementet somewhat like this, Note: Generics can be applied to both a Class or an Interface.

public class NameOfTheClass<E> {
....
public doSome(E e){
    doSomeGenericOperationWith(e);
}

This class could be used like this:

NameOfTheClass<AType> instance = new NameOfTheClass<AType>();
Atype yourType = ...
doSome(yourType);

Note: Any use of the doSome()-method will require a parameter of type Atype, this will be handled by the Java-compiler. So if you try to call the method with some other type, an compile-error will rise.

More readings : http://docs.oracle.com/javase/tutorial/java/generics/why.html