code: public void decrementTargetIncomingTransitionCounts()
      {
          for(Entry<Character, MDAGNode> transitionKeyValuePair: outgoingTransitionTreeMap.entrySet())
              transitionKeyValuePair.getValue().incomingTransitionCount--;
      }
docs: 本状态的目标状态们的入度减一
  Decrements (by 1) the incoming _transition counts of all of the nodes
  that are targets of outgoing transitions from this node.