NullWritable.java
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上传日期:2018-01-08
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文件大小:2k
- /**
- * 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());
- }
- }