/** * Copyright 2005 The Apache Software Foundation * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *     http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package org.apache.hadoop.io;import java.io.DataOutput;import java.io.DataInput;import java.io.IOException;/** A simple, efficient, serialization protocol, based on {@link DataInput} and * {@link DataOutput}. * * <p>Implementations typically implement a static <code>read(DataInput)</code> * method which constructs a new instance, calls {@link * #readFields(DataInput)}, and returns the instance. * * @author Doug Cutting */public interface Writable {  /** Writes the fields of this object to <code>out</code>. */  void write(DataOutput out) throws IOException;  /** Reads the fields of this object from <code>in</code>.  For efficiency,   * implementations should attempt to re-use storage in the existing object   * where possible.   */  void readFields(DataInput in) throws IOException;}