Yes, an unreachable object may become reachable again.This 
happens when the object's finalize() method is invoked and 
the objct performs an operation which causes it to become 
accessible to reachable objects.

YES, Finalization is a feature of the Java programming 
language that allows you to perform postmortem cleanup on 
objects that the garbage collector has found to be 
unreachable. It is typically used to reclaim native 
resources associated with an object. 
When the garbage collector determines that obj is 
unreachable, it notices that obj is finalizable -- as it 
had been recorded upon allocation -- and adds it to the 
JVM's finalization queue. It also ensures that all objects 
reachable from obj are retained, even if they are otherwise 
unreachable, as they might be accessed by the finalizer.

So, we can say that it can be reachable.

yes an unreachable object may become reachable once it get a
reference befre garbage collection especially in finalize()
method call