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| <h2 title="Interface WritableComparable" class="title">Interface WritableComparable<T></h2> |
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| <dt>All Superinterfaces:</dt> |
| <dd><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Comparable.html?is-external=true" title="class or interface in java.lang">Comparable</a><T>, <a href="../../../../org/apache/hadoop/io/Writable.html" title="interface in org.apache.hadoop.io">Writable</a></dd> |
| </dl> |
| <dl> |
| <dt>All Known Implementing Classes:</dt> |
| <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/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/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/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/io/ShortWritable.html" title="class in org.apache.hadoop.io">ShortWritable</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/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> |
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| <br> |
| <pre>@InterfaceAudience.Public |
| @InterfaceStability.Stable |
| public interface <span class="typeNameLabel">WritableComparable<T></span> |
| extends <a href="../../../../org/apache/hadoop/io/Writable.html" title="interface in org.apache.hadoop.io">Writable</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Comparable.html?is-external=true" title="class or interface in java.lang">Comparable</a><T></pre> |
| <div class="block">A <a href="../../../../org/apache/hadoop/io/Writable.html" title="interface in org.apache.hadoop.io"><code>Writable</code></a> which is also <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Comparable.html?is-external=true" title="class or interface in java.lang"><code>Comparable</code></a>. |
| |
| <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> |
| <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></div> |
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| <code><a href="../../../../org/apache/hadoop/io/Writable.html#readFields-java.io.DataInput-">readFields</a>, <a href="../../../../org/apache/hadoop/io/Writable.html#write-java.io.DataOutput-">write</a></code></li> |
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| <code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Comparable.html?is-external=true#compareTo-T-" title="class or interface in java.lang">compareTo</a></code></li> |
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