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7WritableComparable (Hadoop 0.20.1 API)
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91org.apache.hadoop.io</FONT>
92<BR>
93Interface WritableComparable&lt;T&gt;</H2>
94<DL>
95<DT><B>All Superinterfaces:</B> <DD><A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Comparable.html?is-external=true" title="class or interface in java.lang">Comparable</A>&lt;T&gt;, <A HREF="../../../../org/apache/hadoop/io/Writable.html" title="interface in org.apache.hadoop.io">Writable</A></DD>
96</DL>
97<DL>
98<DT><B>All Known Implementing Classes:</B> <DD><A HREF="../../../../org/apache/hadoop/io/BooleanWritable.html" title="class in org.apache.hadoop.io">BooleanWritable</A>, <A HREF="../../../../org/apache/hadoop/io/BytesWritable.html" title="class in org.apache.hadoop.io">BytesWritable</A>, <A HREF="../../../../org/apache/hadoop/io/ByteWritable.html" title="class in org.apache.hadoop.io">ByteWritable</A>, <A HREF="../../../../org/apache/hadoop/contrib/index/mapred/DocumentID.html" title="class in org.apache.hadoop.contrib.index.mapred">DocumentID</A>, <A HREF="../../../../org/apache/hadoop/io/DoubleWritable.html" title="class in org.apache.hadoop.io">DoubleWritable</A>, <A HREF="../../../../org/apache/hadoop/io/FloatWritable.html" title="class in org.apache.hadoop.io">FloatWritable</A>, <A HREF="../../../../org/apache/hadoop/mapreduce/ID.html" title="class in org.apache.hadoop.mapreduce">ID</A>, <A HREF="../../../../org/apache/hadoop/mapred/ID.html" title="class in org.apache.hadoop.mapred">ID</A>, <A HREF="../../../../org/apache/hadoop/io/IntWritable.html" title="class in org.apache.hadoop.io">IntWritable</A>, <A HREF="../../../../org/apache/hadoop/mapreduce/JobID.html" title="class in org.apache.hadoop.mapreduce">JobID</A>, <A HREF="../../../../org/apache/hadoop/mapred/JobID.html" title="class in org.apache.hadoop.mapred">JobID</A>, <A HREF="../../../../org/apache/hadoop/util/bloom/Key.html" title="class in org.apache.hadoop.util.bloom">Key</A>, <A HREF="../../../../org/apache/hadoop/io/LongWritable.html" title="class in org.apache.hadoop.io">LongWritable</A>, <A HREF="../../../../org/apache/hadoop/io/MD5Hash.html" title="class in org.apache.hadoop.io">MD5Hash</A>, <A HREF="../../../../org/apache/hadoop/examples/MultiFileWordCount.WordOffset.html" title="class in org.apache.hadoop.examples">MultiFileWordCount.WordOffset</A>, <A HREF="../../../../org/apache/hadoop/io/NullWritable.html" title="class in org.apache.hadoop.io">NullWritable</A>, <A HREF="../../../../org/apache/hadoop/record/Record.html" title="class in org.apache.hadoop.record">Record</A>, <A HREF="../../../../org/apache/hadoop/record/meta/RecordTypeInfo.html" title="class in org.apache.hadoop.record.meta">RecordTypeInfo</A>, <A HREF="../../../../org/apache/hadoop/examples/SecondarySort.IntPair.html" title="class in org.apache.hadoop.examples">SecondarySort.IntPair</A>, <A HREF="../../../../org/apache/hadoop/contrib/index/mapred/Shard.html" title="class in org.apache.hadoop.contrib.index.mapred">Shard</A>, <A HREF="../../../../org/apache/hadoop/mapreduce/TaskAttemptID.html" title="class in org.apache.hadoop.mapreduce">TaskAttemptID</A>, <A HREF="../../../../org/apache/hadoop/mapred/TaskAttemptID.html" title="class in org.apache.hadoop.mapred">TaskAttemptID</A>, <A HREF="../../../../org/apache/hadoop/mapreduce/TaskID.html" title="class in org.apache.hadoop.mapreduce">TaskID</A>, <A HREF="../../../../org/apache/hadoop/mapred/TaskID.html" title="class in org.apache.hadoop.mapred">TaskID</A>, <A HREF="../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</A>, <A HREF="../../../../org/apache/hadoop/io/UTF8.html" title="class in org.apache.hadoop.io">UTF8</A>, <A HREF="../../../../org/apache/hadoop/io/VIntWritable.html" title="class in org.apache.hadoop.io">VIntWritable</A>, <A HREF="../../../../org/apache/hadoop/io/VLongWritable.html" title="class in org.apache.hadoop.io">VLongWritable</A></DD>
99</DL>
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102<DT><PRE>public interface <B>WritableComparable&lt;T&gt;</B><DT>extends <A HREF="../../../../org/apache/hadoop/io/Writable.html" title="interface in org.apache.hadoop.io">Writable</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Comparable.html?is-external=true" title="class or interface in java.lang">Comparable</A>&lt;T&gt;</DL>
103</PRE>
104
105<P>
106A <A HREF="../../../../org/apache/hadoop/io/Writable.html" title="interface in org.apache.hadoop.io"><CODE>Writable</CODE></A> which is also <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Comparable.html?is-external=true" title="class or interface in java.lang"><CODE>Comparable</CODE></A>.
107
108 <p><code>WritableComparable</code>s can be compared to each other, typically
109 via <code>Comparator</code>s. Any type which is to be used as a
110 <code>key</code> in the Hadoop Map-Reduce framework should implement this
111 interface.</p>
112 
113 <p>Example:</p>
114 <p><blockquote><pre>
115     public class MyWritableComparable implements WritableComparable {
116       // Some data
117       private int counter;
118       private long timestamp;
119       
120       public void write(DataOutput out) throws IOException {
121         out.writeInt(counter);
122         out.writeLong(timestamp);
123       }
124       
125       public void readFields(DataInput in) throws IOException {
126         counter = in.readInt();
127         timestamp = in.readLong();
128       }
129       
130       public int compareTo(MyWritableComparable w) {
131         int thisValue = this.value;
132         int thatValue = ((IntWritable)o).value;
133         return (thisValue &lt; thatValue ? -1 : (thisValue==thatValue ? 0 : 1));
134       }
135     }
136 </pre></blockquote></p>
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