instantiated objects of one class

Well, the Class class doesn't define such a method, so I would think there isn't one. You can have a static Vector for your class and add each instance to it on construction and remove it on destruction (finalize()).

finalize() is not always guaranteed to be called,for threads at least.

Thread t=new Thread();
Thread [] currentThreads= new Thread [t.activeCount()];
t.enumerate(currentThreads);

there maybe a method to do it

A. AFAIK finalize() is guaranteed to be called, just the exact time is not guaranteed to be anything.
B. >> At runtime, is there a way to get the references of all
>> objects that are instances of one given class?
What's up with the thread count? The question was about instances of a class.

Ok, I see what you mean now :-)
But I think that will only give you the active (running) Threads, not all instances of class Thread.

>>>>>At runtime, is there a way to get the references of all objects that are instances of one given class?

Yes Sasha_M I dont know how to get all other objects ,but I think for all threads at least you can keep track of thru this method.