001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    
019    package org.apache.hadoop.conf;
020    
021    import java.util.Collection;
022    
023    /**
024     * Something whose {@link Configuration} can be changed at run time.
025     */
026    public interface Reconfigurable extends Configurable {
027    
028      /**
029       * Change a configuration property on this object to the value specified.
030       *
031       * Change a configuration property on this object to the value specified 
032       * and return the previous value that the configuration property was set to
033       * (or null if it was not previously set). If newVal is null, set the property
034       * to its default value;
035       *
036       * If the property cannot be changed, throw a 
037       * {@link ReconfigurationException}.
038       */
039      public String reconfigureProperty(String property, String newVal) 
040        throws ReconfigurationException;
041    
042      /**
043       * Return whether a given property is changeable at run time.
044       *
045       * If isPropertyReconfigurable returns true for a property,
046       * then changeConf should not throw an exception when changing
047       * this property.
048       */
049      public boolean isPropertyReconfigurable(String property);
050    
051      /**
052       * Return all the properties that can be changed at run time.
053       */
054      public Collection<String> getReconfigurableProperties();
055    
056    
057    }