Implementation of Runnable has the advantage (and in some cases the only possible option) of allowing the implementation to extend another class. It is particularly helpful when you would like to add thread-like behavior to an existing class. Implementing Runnable allows more flexibility in usage. But otherwise, there is no difference in functionality comparing to the extending of the Thread class.
Thread class has several constructors that allow setting the thread name and the group it belongs to. Grouping of threads helps to manage them in the case of many threads running in parallel. Thread class has also several methods that provide information about the thread's status, its properties, and allows to control its behavior.
As you have seen, the thread's ID is generated automatically. It cannot be changed but can be reused...
