I think that means we do not have the name of the variable that is used to reference this object in the parent object. the parent object is your HashMap@1703521. It has a field that references your ExecuteThread object. We try to capture the field name but in some cases we cant get it. Thats when we display ?
Andy, thanks for your reply. I am trying to follow the references for the big object: java.langObject@4698097, to find out why it's not GCed, but when tracking to the ExecuteThread object, I can't find the field name that reference the HashMap@1703521 object in ExecuteThread, and I have no idea as why this big object is not GCed due to the missing reference chain to the VM root, do you have any suggestion on how to solve such problem?