java.lang.ThreadGroup[name=main,maxpri=10]
  java.lang.ThreadGroup[name=system,maxpri=10]
  main
  10
  false
java.lang.ThreadGroup[name=system,maxpri=10]
  null
  system
  10
  false
main:
  [Thread[main,5,main]]
  []
system:
  [Thread[FinalizerDaemon,5,system], Thread[FinalizerWatchdogDaemon,5,system], Thread[HeapTaskDaemon,5,system], Thread[ReferenceQueueDaemon,5,system], Thread[Signal Catcher,5,system]]
  [java.lang.ThreadGroup[name=main,maxpri=10]]