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Defines buffers, which are containers for data, and provides an overview of the
other NIO packages.


<p> The central abstractions of the NIO APIs are: </p>

<ul>

  <li><p> <a href="#buffers"><i>Buffers</i></a>, which are containers for data;
  </p></li>

  <li><p> <a href="charset/package-summary.html"><i>Charsets</i></a> and their
  associated <i>decoders</i> and <i>encoders</i>, <br> which translate between
  bytes and Unicode characters; </p></li>

  <li><p> <a href="channels/package-summary.html"><i>Channels</i></a> of
  various types, which represent connections <br> to entities capable of
  performing I/O operations; and </p></li>

  <li><p> <i>Selectors</i> and <i>selection keys</i>, which together with <br>
  <i>selectable channels</i> define a <a
  href="channels/package-summary.html#multiplex">multiplexed, non-blocking <br>
  I/O</a>&nbsp;facility.  </p></li>

</ul>

<p> The <tt>java.nio</tt> package defines the buffer classes, which are used
throughout the NIO APIs.  The charset API is defined in the {@link
java.nio.charset} package, and the channel and selector APIs are defined in the
{@link java.nio.channels} package.  Each of these subpackages has its own
service-provider (SPI) subpackage, the contents of which can be used to extend
the platform's default implementations or to construct alternative
implementations.


<a name="buffers">

<blockquote><table cellspacing=1 cellpadding=0 summary="Description of the various buffers">
  <tr><th><p align="left">Buffers</p></th><th><p align="left">Description</p></th></tr> 
  <tr><td valign=top><tt>{@link java.nio.Buffer}</tt></td>
      <td>Position, limit, and capacity;
          <br>clear, flip, rewind, and mark/reset</td></tr>
  <tr><td valign=top><tt>&nbsp;&nbsp;{@link java.nio.ByteBuffer}</tt></td>
      <td>Get/put, compact, views; allocate,&nbsp;wrap</td></tr>
  <tr><td valign=top><tt>&nbsp;&nbsp;&nbsp;&nbsp;{@link java.nio.MappedByteBuffer}&nbsp;&nbsp;</tt></td>
      <td>A byte buffer mapped to a file</td></tr>
  <tr><td valign=top><tt>&nbsp;&nbsp;{@link java.nio.CharBuffer}</tt></td>
      <td>Get/put, compact; allocate,&nbsp;wrap</td></tr>
  <tr><td valign=top><tt>&nbsp;&nbsp;{@link java.nio.DoubleBuffer}</tt></td>
      <td>&nbsp;&nbsp;&nbsp;&nbsp;'&nbsp;'</td></tr>
  <tr><td valign=top><tt>&nbsp;&nbsp;{@link java.nio.FloatBuffer}</tt></td>
      <td>&nbsp;&nbsp;&nbsp;&nbsp;'&nbsp;'</td></tr>
  <tr><td valign=top><tt>&nbsp;&nbsp;{@link java.nio.IntBuffer}</tt></td>
      <td>&nbsp;&nbsp;&nbsp;&nbsp;'&nbsp;'</td></tr>
  <tr><td valign=top><tt>&nbsp;&nbsp;{@link java.nio.LongBuffer}</tt></td>
      <td>&nbsp;&nbsp;&nbsp;&nbsp;'&nbsp;'</td></tr>
  <tr><td valign=top><tt>&nbsp;&nbsp;{@link java.nio.ShortBuffer}</tt></td>
      <td>&nbsp;&nbsp;&nbsp;&nbsp;'&nbsp;'</td></tr>
  <tr><td valign=top><tt>{@link java.nio.ByteOrder}</tt></td>
      <td>Typesafe enumeration for&nbsp;byte&nbsp;orders</td></tr>
</table></blockquote>

<p> A <i>buffer</i> is a container for a fixed amount of data of a specific
primitive type.  In addition to its content a buffer has a <i>position</i>,
which is the index of the next element to be read or written, and a
<i>limit</i>, which is the index of the first element that should not be read
or written.  The base {@link java.nio.Buffer} class defines these properties as
well as methods for <i>clearing</i>, <i>flipping</i>, and <i>rewinding</i>, for
<i>marking</i> the current position, and for <i>resetting</i> the position to
the previous mark.

<p> There is a buffer class for each non-boolean primitive type.  Each class
defines a family of <i>get</i> and <i>put</i> methods for moving data out of
and in to a buffer, methods for <i>compacting</i>, <i>duplicating</i>, and
<i>slicing</i> a buffer, and static methods for <i>allocating</i> a new buffer
as well as for <i>wrapping</i> an existing array into a buffer.

<p> Byte buffers are distinguished in that they can be used as the sources and
targets of I/O operations.  They also support several features not found in the
other buffer classes:

<ul>

  <li><p> A byte buffer can be allocated as a <a href="ByteBuffer.html#direct">
  <i>direct</i></a> buffer, in which case the Java virtual machine will make a
  best effort to perform native I/O operations directly upon it.  </p></li>

  <li><p> A byte buffer can be created by {@link
  java.nio.channels.FileChannel#map </code><i>mapping</i><code>} a region of a
  file directly into memory, in which case a few additional file-related
  operations defined in the {@link java.nio.MappedByteBuffer} class are
  available.  </p></li>

  <li><p> A byte buffer provides access to its content as either a heterogeneous
  or homogeneous sequence of <a href="ByteBuffer.html#bin">binary data</i></a>
  of any non-boolean primitive type, in either big-endian or little-endian <a
  href="ByteOrder.html">byte order</a>.  </p></li>

</ul>

<p> Unless otherwise noted, passing a <tt>null</tt> argument to a constructor
or method in any class or interface in this package will cause a {@link
java.lang.NullPointerException NullPointerException} to be thrown.

@since 1.4
@author Mark Reinhold
@author JSR-51 Expert Group

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