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| 25 | |||
| 26 | <!doctype html public "-//IETF//DTD HTML//EN"> | ||
| 27 | <html> | ||
| 28 | <body bgcolor="white"> | ||
| 29 | |||
| 30 | Defines buffers, which are containers for data, and provides an overview of the | ||
| 31 | other NIO packages. | ||
| 32 | |||
| 33 | |||
| 34 | <p> The central abstractions of the NIO APIs are: </p> | ||
| 35 | |||
| 36 | <ul> | ||
| 37 | |||
| 38 | <li><p> <a href="#buffers"><i>Buffers</i></a>, which are containers for data; | ||
| 39 | </p></li> | ||
| 40 | |||
| 41 | <li><p> <a href="charset/package-summary.html"><i>Charsets</i></a> and their | ||
| 42 | associated <i>decoders</i> and <i>encoders</i>, <br> which translate between | ||
| 43 | bytes and Unicode characters; </p></li> | ||
| 44 | |||
| 45 | <li><p> <a href="channels/package-summary.html"><i>Channels</i></a> of | ||
| 46 | various types, which represent connections <br> to entities capable of | ||
| 47 | performing I/O operations; and </p></li> | ||
| 48 | |||
| 49 | <li><p> <i>Selectors</i> and <i>selection keys</i>, which together with <br> | ||
| 50 | <i>selectable channels</i> define a <a | ||
| 51 | href="channels/package-summary.html#multiplex">multiplexed, non-blocking <br> | ||
| 52 | I/O</a> facility. </p></li> | ||
| 53 | |||
| 54 | </ul> | ||
| 55 | |||
| 56 | <p> The <tt>java.nio</tt> package defines the buffer classes, which are used | ||
| 57 | throughout the NIO APIs. The charset API is defined in the {@link | ||
| 58 | java.nio.charset} package, and the channel and selector APIs are defined in the | ||
| 59 | {@link java.nio.channels} package. Each of these subpackages has its own | ||
| 60 | service-provider (SPI) subpackage, the contents of which can be used to extend | ||
| 61 | the platform's default implementations or to construct alternative | ||
| 62 | implementations. | ||
| 63 | |||
| 64 | |||
| 65 | <a name="buffers"> | ||
| 66 | |||
| 67 | <blockquote><table cellspacing=1 cellpadding=0 summary="Description of the various buffers"> | ||
| 68 | <tr><th><p align="left">Buffers</p></th><th><p align="left">Description</p></th></tr> | ||
| 69 | <tr><td valign=top><tt>{@link java.nio.Buffer}</tt></td> | ||
| 70 | <td>Position, limit, and capacity; | ||
| 71 | <br>clear, flip, rewind, and mark/reset</td></tr> | ||
| 72 | <tr><td valign=top><tt> {@link java.nio.ByteBuffer}</tt></td> | ||
| 73 | <td>Get/put, compact, views; allocate, wrap</td></tr> | ||
| 74 | <tr><td valign=top><tt> {@link java.nio.MappedByteBuffer} </tt></td> | ||
| 75 | <td>A byte buffer mapped to a file</td></tr> | ||
| 76 | <tr><td valign=top><tt> {@link java.nio.CharBuffer}</tt></td> | ||
| 77 | <td>Get/put, compact; allocate, wrap</td></tr> | ||
| 78 | <tr><td valign=top><tt> {@link java.nio.DoubleBuffer}</tt></td> | ||
| 79 | <td> ' '</td></tr> | ||
| 80 | <tr><td valign=top><tt> {@link java.nio.FloatBuffer}</tt></td> | ||
| 81 | <td> ' '</td></tr> | ||
| 82 | <tr><td valign=top><tt> {@link java.nio.IntBuffer}</tt></td> | ||
| 83 | <td> ' '</td></tr> | ||
| 84 | <tr><td valign=top><tt> {@link java.nio.LongBuffer}</tt></td> | ||
| 85 | <td> ' '</td></tr> | ||
| 86 | <tr><td valign=top><tt> {@link java.nio.ShortBuffer}</tt></td> | ||
| 87 | <td> ' '</td></tr> | ||
| 88 | <tr><td valign=top><tt>{@link java.nio.ByteOrder}</tt></td> | ||
| 89 | <td>Typesafe enumeration for byte orders</td></tr> | ||
| 90 | </table></blockquote> | ||
| 91 | |||
| 92 | <p> A <i>buffer</i> is a container for a fixed amount of data of a specific | ||
| 93 | primitive type. In addition to its content a buffer has a <i>position</i>, | ||
| 94 | which is the index of the next element to be read or written, and a | ||
| 95 | <i>limit</i>, which is the index of the first element that should not be read | ||
| 96 | or written. The base {@link java.nio.Buffer} class defines these properties as | ||
| 97 | well as methods for <i>clearing</i>, <i>flipping</i>, and <i>rewinding</i>, for | ||
| 98 | <i>marking</i> the current position, and for <i>resetting</i> the position to | ||
| 99 | the previous mark. | ||
| 100 | |||
| 101 | <p> There is a buffer class for each non-boolean primitive type. Each class | ||
| 102 | defines a family of <i>get</i> and <i>put</i> methods for moving data out of | ||
| 103 | and in to a buffer, methods for <i>compacting</i>, <i>duplicating</i>, and | ||
| 104 | <i>slicing</i> a buffer, and static methods for <i>allocating</i> a new buffer | ||
| 105 | as well as for <i>wrapping</i> an existing array into a buffer. | ||
| 106 | |||
| 107 | <p> Byte buffers are distinguished in that they can be used as the sources and | ||
| 108 | targets of I/O operations. They also support several features not found in the | ||
| 109 | other buffer classes: | ||
| 110 | |||
| 111 | <ul> | ||
| 112 | |||
| 113 | <li><p> A byte buffer can be allocated as a <a href="ByteBuffer.html#direct"> | ||
| 114 | <i>direct</i></a> buffer, in which case the Java virtual machine will make a | ||
| 115 | best effort to perform native I/O operations directly upon it. </p></li> | ||
| 116 | |||
| 117 | <li><p> A byte buffer can be created by {@link | ||
| 118 | java.nio.channels.FileChannel#map </code><i>mapping</i><code>} a region of a | ||
| 119 | file directly into memory, in which case a few additional file-related | ||
| 120 | operations defined in the {@link java.nio.MappedByteBuffer} class are | ||
| 121 | available. </p></li> | ||
| 122 | |||
| 123 | <li><p> A byte buffer provides access to its content as either a heterogeneous | ||
| 124 | or homogeneous sequence of <a href="ByteBuffer.html#bin">binary data</i></a> | ||
| 125 | of any non-boolean primitive type, in either big-endian or little-endian <a | ||
| 126 | href="ByteOrder.html">byte order</a>. </p></li> | ||
| 127 | |||
| 128 | </ul> | ||
| 129 | |||
| 130 | <p> Unless otherwise noted, passing a <tt>null</tt> argument to a constructor | ||
| 131 | or method in any class or interface in this package will cause a {@link | ||
| 132 | java.lang.NullPointerException NullPointerException} to be thrown. | ||
| 133 | |||
| 134 | @since 1.4 | ||
| 135 | @author Mark Reinhold | ||
| 136 | @author JSR-51 Expert Group | ||
| 137 | |||
| 138 | </body> | ||
| 139 | </html> | ||