errors

org.apache.zookeeper.KeeperException$NodeExistsException: KeeperErrorCode = NodeExists for /master
at org.apache.zookeeper.KeeperException.create(KeeperException.java:119)
at org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
at org.apache.zookeeper.ZooKeeper.create(ZooKeeper.java:783)
at yangqi.zookeeper.example.masterworker.Master.createMaterNode(Master.java:64)
2016-01-08 20:58:20,385 [myid:] - INFO [pool-1-thread-2:ZooKeeper@684] - Session: 0x15215be52dc0005 closed
at yangqi.zookeeper.example.masterworker.Master.registerForMaster(Master.java:90)
2016-01-08 20:58:20,385 [myid:] - INFO [pool-1-thread-2-EventThread:ClientCnxn$EventThread@509] - EventThread shut down
at yangqi.zookeeper.example.masterworker.Master.run(Master.java:107)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
org.apache.zookeeper.KeeperException$NoNodeException: KeeperErrorCode = NoNode for /master