In a clean design object in a given tree should be used with an uniform interface. Your doubts reflects a design smell.
The goal of having object trees in scenes is to be able to apply geometric transformations to a group of objects. So if you have objects that can't move, they don't belong to the tree. It does not make sense.
Here is a possible solution. You can have a render class which can have background objects, and the root of the movable objects. All the movable objects can move. A transformation applied to an object is propagated to its children.
To render the scene, you have to render both the unmovable background objects, and the actual scene by calling a render function on the root.
Declaring immutable class final saves programmer from the need to repeat declaring final in each and every method declaration, over and over and over again.
In classes like java.lang.String, having over 60 methods, this is substantial save, as well as important guarantee that necessary modifier won't be omitted by mistake.
When object is intended to be immutable, mistakes to declare final method may be hard to detect, because there is no reliable way to tell whether programmer omitted final modifier intentionally or by mistake.
final classes have no real purpose except perhaps brevity
Besides brevity and helping to avoid mistakes, a strong benefit of declaring immutable class final is that this makes programmer's intent explicit, unambiguously communicating to API users that none of class methods are intended for override.
Alternative way, that is, declaring all methods final, lacks this important "feature", as it leaves users of the API in the indecisive state, whether API designers intended to only protect some methods from overloading, and it only accidentally turned out that all of them got final, or there was a design decision to cover all the class.
my opinion is that final classes are superfluous as final methods are all you need
Given above, having final modifier for class doesn't look superfluous to me.
It is worth noting that Sun/Oracle Java tutorial presents final classes as a matter of usefulness and not as that of convenience. If final classes purpose was mere brevity / syntactic sugar, one would expect tutorial to explain these as convenience.
...you can also declare an entire class final. A class that is declared final cannot be subclassed. This is particularly useful, for example, when creating an immutable class like the String class.
Best Answer
Whoever wrote that is wrong. Use
finalliberally, there’s nothing wrong with that. It documents that a class wasn’t designed with inheritance in mind, and this is usually true for all classes by default: designing a class that can be meaningfully inherited from takes more than just removing afinalspecifier; it takes a lot of care.So using
finalby default is by no means bad. In fact, many people propose that this should be the default, e.g. Jon Skeet.This is indeed a caveat, but you can always recourse to interfaces if you need to mock your classes. This is certainly superior to making all classes open to inheritance just for the purpose of mocking.