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<div class="subTitle">org.apache.hadoop.io</div>
<h2 title="Interface Writable" class="title">Interface Writable</h2>
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<dt>All Known Subinterfaces:</dt>
<dd><a href="../../../../org/apache/hadoop/io/WritableComparable.html" title="interface in org.apache.hadoop.io">WritableComparable</a>&lt;T&gt;</dd>
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<dt>All Known Implementing Classes:</dt>
<dd><a href="../../../../org/apache/hadoop/security/token/delegation/AbstractDelegationTokenIdentifier.html" title="class in org.apache.hadoop.security.token.delegation">AbstractDelegationTokenIdentifier</a>, <a href="../../../../org/apache/hadoop/io/AbstractMapWritable.html" title="class in org.apache.hadoop.io">AbstractMapWritable</a>, <a href="../../../../org/apache/hadoop/security/authorize/AccessControlList.html" title="class in org.apache.hadoop.security.authorize">AccessControlList</a>, <a href="../../../../org/apache/hadoop/io/ArrayPrimitiveWritable.html" title="class in org.apache.hadoop.io">ArrayPrimitiveWritable</a>, <a href="../../../../org/apache/hadoop/io/ArrayWritable.html" title="class in org.apache.hadoop.io">ArrayWritable</a>, <a href="../../../../org/apache/hadoop/util/bloom/BloomFilter.html" title="class in org.apache.hadoop.util.bloom">BloomFilter</a>, <a href="../../../../org/apache/hadoop/io/BooleanWritable.html" title="class in 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<pre>@InterfaceAudience.Public
@InterfaceStability.Stable
public interface <span class="typeNameLabel">Writable</span></pre>
<div class="block">A serializable object which implements a simple, efficient, serialization
protocol, based on <a href="https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html?is-external=true" title="class or interface in java.io"><code>DataInput</code></a> and <a href="https://docs.oracle.com/javase/8/docs/api/java/io/DataOutput.html?is-external=true" title="class or interface in java.io"><code>DataOutput</code></a>.
<p>Any <code>key</code> or <code>value</code> type in the Hadoop Map-Reduce
framework implements this interface.</p>
<p>Implementations typically implement a static <code>read(DataInput)</code>
method which constructs a new instance, calls <a href="../../../../org/apache/hadoop/io/Writable.html#readFields-java.io.DataInput-"><code>readFields(DataInput)</code></a>
and returns the instance.</p>
<p>Example:</p>
<blockquote><pre>
public class MyWritable implements Writable {
// Some data
private int counter;
private long timestamp;
// Default constructor to allow (de)serialization
MyWritable() { }
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 static MyWritable read(DataInput in) throws IOException {
MyWritable w = new MyWritable();
w.readFields(in);
return w;
}
}
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<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/hadoop/io/Writable.html#readFields-java.io.DataInput-">readFields</a></span>(<a href="https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html?is-external=true" title="class or interface in java.io">DataInput</a>&nbsp;in)</code>
<div class="block">Deserialize the fields of this object from <code>in</code>.</div>
</td>
</tr>
<tr id="i1" class="rowColor">
<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/hadoop/io/Writable.html#write-java.io.DataOutput-">write</a></span>(<a href="https://docs.oracle.com/javase/8/docs/api/java/io/DataOutput.html?is-external=true" title="class or interface in java.io">DataOutput</a>&nbsp;out)</code>
<div class="block">Serialize the fields of this object to <code>out</code>.</div>
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<h4>write</h4>
<pre>void&nbsp;write(<a href="https://docs.oracle.com/javase/8/docs/api/java/io/DataOutput.html?is-external=true" title="class or interface in java.io">DataOutput</a>&nbsp;out)
throws <a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></pre>
<div class="block">Serialize the fields of this object to <code>out</code>.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>out</code> - <code>DataOuput</code> to serialize this object into.</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></code></dd>
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<h4>readFields</h4>
<pre>void&nbsp;readFields(<a href="https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html?is-external=true" title="class or interface in java.io">DataInput</a>&nbsp;in)
throws <a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></pre>
<div class="block">Deserialize the fields of this object from <code>in</code>.
<p>For efficiency, implementations should attempt to re-use storage in the
existing object where possible.</p></div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>in</code> - <code>DataInput</code> to deseriablize this object from.</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></code></dd>
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