It's not for a real-life programming
I just wanted to find out some opportunity to check my SCJP 6 answers
I assumed, maybe there exists some real-time list of objects with attribute: this object is accessible or not accessible for GC.
Alex, I see from some of your other posts that you're concentrating on the certification exam. You'll definitely find questions about when objects become eligible for garbage collection on that exam, but those questions are simply designed to test your knowledge of how object references work in Java. However don't confuse the questions with anything related to real-life programming. Don't take the examples you see there to be examples of good Java code (they are often examples of bad Java code designed to test your knowledge) and don't take the questions to be questions which you will actually encounter when you are writing code.