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.mapreduce;
020    
021    import java.io.DataInput;
022    import java.io.DataOutput;
023    import java.io.IOException;
024    
025    import org.apache.hadoop.classification.InterfaceAudience;
026    import org.apache.hadoop.classification.InterfaceStability;
027    import org.apache.hadoop.io.WritableComparable;
028    
029    /**
030     * A general identifier, which internally stores the id
031     * as an integer. This is the super class of {@link JobID}, 
032     * {@link TaskID} and {@link TaskAttemptID}.
033     * 
034     * @see JobID
035     * @see TaskID
036     * @see TaskAttemptID
037     */
038    @InterfaceAudience.Public
039    @InterfaceStability.Stable
040    public abstract class ID implements WritableComparable<ID> {
041      protected static final char SEPARATOR = '_';
042      protected int id;
043    
044      /** constructs an ID object from the given int */
045      public ID(int id) {
046        this.id = id;
047      }
048    
049      protected ID() {
050      }
051    
052      /** returns the int which represents the identifier */
053      public int getId() {
054        return id;
055      }
056    
057      @Override
058      public String toString() {
059        return String.valueOf(id);
060      }
061    
062      @Override
063      public int hashCode() {
064        return id;
065      }
066    
067      @Override
068      public boolean equals(Object o) {
069        if (this == o)
070          return true;
071        if(o == null)
072          return false;
073        if (o.getClass() == this.getClass()) {
074          ID that = (ID) o;
075          return this.id == that.id;
076        }
077        else
078          return false;
079      }
080    
081      /** Compare IDs by associated numbers */
082      public int compareTo(ID that) {
083        return this.id - that.id;
084      }
085    
086      public void readFields(DataInput in) throws IOException {
087        this.id = in.readInt();
088      }
089    
090      public void write(DataOutput out) throws IOException {
091        out.writeInt(id);
092      }
093      
094    }