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1   /**
2    * Copyright 2010 The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *     http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  package org.apache.hadoop.hbase.zookeeper;
21  
22  
23  /**
24   * Base class for internal listeners of ZooKeeper events.
25   *
26   * The {@link ZooKeeperWatcher} for a process will execute the appropriate
27   * methods of implementations of this class.  In order to receive events from
28   * the watcher, every listener must register itself via {@link ZooKeeperWatcher#registerListener}.
29   *
30   * Subclasses need only override those methods in which they are interested.
31   *
32   * Note that the watcher will be blocked when invoking methods in listeners so
33   * they must not be long-running.
34   */
35  public abstract class ZooKeeperListener {
36  
37    // Reference to the zk watcher which also contains configuration and constants
38    protected ZooKeeperWatcher watcher;
39  
40    /**
41     * Construct a ZooKeeper event listener.
42     */
43    public ZooKeeperListener(ZooKeeperWatcher watcher) {
44      this.watcher = watcher;
45    }
46  
47    /**
48     * Called when a new node has been created.
49     * @param path full path of the new node
50     */
51    public void nodeCreated(String path) {
52      // no-op
53    }
54  
55    /**
56     * Called when a node has been deleted
57     * @param path full path of the deleted node
58     */
59    public void nodeDeleted(String path) {
60      // no-op
61    }
62  
63    /**
64     * Called when an existing node has changed data.
65     * @param path full path of the updated node
66     */
67    public void nodeDataChanged(String path) {
68      // no-op
69    }
70  
71    /**
72     * Called when an existing node has a child node added or removed.
73     * @param path full path of the node whose children have changed
74     */
75    public void nodeChildrenChanged(String path) {
76      // no-op
77    }
78  }