| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you 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 org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| |
| /** |
| * A {@link Writable} which is also {@link Comparable}. |
| * |
| * <p><code>WritableComparable</code>s can be compared to each other, typically |
| * via <code>Comparator</code>s. Any type which is to be used as a |
| * <code>key</code> in the Hadoop Map-Reduce framework should implement this |
| * interface.</p> |
| * |
| * <p>Note that <code>hashCode()</code> is frequently used in Hadoop to partition |
| * keys. It's important that your implementation of hashCode() returns the same |
| * result across different instances of the JVM. Note also that the default |
| * <code>hashCode()</code> implementation in <code>Object</code> does <b>not</b> |
| * satisfy this property.</p> |
| * |
| * <p>Example:</p> |
| * <p><blockquote><pre> |
| * public class MyWritableComparable implements WritableComparable<MyWritableComparable> { |
| * // Some data |
| * private int counter; |
| * private long timestamp; |
| * |
| * public void write(DataOutput out) throws IOException { |
| * out.writeInt(counter); |
| * out.writeLong(timestamp); |
| * } |
| * |
| * public void readFields(DataInput in) throws IOException { |
| * counter = in.readInt(); |
| * timestamp = in.readLong(); |
| * } |
| * |
| * public int compareTo(MyWritableComparable o) { |
| * int thisValue = this.value; |
| * int thatValue = o.value; |
| * return (thisValue < thatValue ? -1 : (thisValue==thatValue ? 0 : 1)); |
| * } |
| * |
| * public int hashCode() { |
| * final int prime = 31; |
| * int result = 1; |
| * result = prime * result + counter; |
| * result = prime * result + (int) (timestamp ^ (timestamp >>> 32)); |
| * return result |
| * } |
| * } |
| * </pre></blockquote></p> |
| */ |
| @InterfaceAudience.Public |
| @InterfaceStability.Stable |
| public interface WritableComparable<T> extends Writable, Comparable<T> { |
| } |