| /** |
| * 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 java.io.*; |
| |
| /** Singleton Writable with no data. */ |
| public class NullWritable implements WritableComparable { |
| |
| private static final NullWritable THIS = new NullWritable(); |
| |
| private NullWritable() {} // no public ctor |
| |
| /** Returns the single instance of this class. */ |
| public static NullWritable get() { return THIS; } |
| |
| public String toString() { |
| return "(null)"; |
| } |
| |
| public int hashCode() { return 0; } |
| public int compareTo(Object other) { |
| if (!(other instanceof NullWritable)) { |
| throw new ClassCastException("can't compare " + other.getClass().getName() |
| + " to NullWritable"); |
| } |
| return 0; |
| } |
| public boolean equals(Object other) { return other instanceof NullWritable; } |
| public void readFields(DataInput in) throws IOException {} |
| public void write(DataOutput out) throws IOException {} |
| |
| /** A Comparator "optimized" for NullWritable. */ |
| public static class Comparator extends WritableComparator { |
| public Comparator() { |
| super(NullWritable.class); |
| } |
| |
| /** |
| * Compare the buffers in serialized form. |
| */ |
| public int compare(byte[] b1, int s1, int l1, |
| byte[] b2, int s2, int l2) { |
| assert 0 == l1; |
| assert 0 == l2; |
| return 0; |
| } |
| } |
| |
| static { // register this comparator |
| WritableComparator.define(NullWritable.class, new Comparator()); |
| } |
| } |
| |