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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"> </a>
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 <i>mapping</i>} 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>