1 /* 2 * Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 /** 27 * Defines buffers, which are containers for data, and provides an 28 * overview of the other NIO packages. 29 * 30 * 31 * <p> The central abstractions of the NIO APIs are: </p> 32 * 33 * <ul> 34 * 35 * <li><p> <a href="#buffers"><i>Buffers</i></a>, which are containers for data; 36 * </p></li> 37 * 38 * <li><p> <a 39 * href="charset/package-summary.html"><i>Charsets</i></a> and their 40 * associated <i>decoders</i> and <i>encoders</i>, <br> which 41 * translate between bytes and Unicode characters; </p></li> 42 * 43 * <li><p> <a 44 * href="channels/package-summary.html"><i>Channels</i></a> of 45 * various types, which represent connections <br> to entities 46 * capable of performing I/O operations; and </p></li> 47 * 48 * <li><p> <i>Selectors</i> and <i>selection keys</i>, which 49 * together with <br> <i>selectable channels</i> define a <a 50 * href="channels/package-summary.html#multiplex">multiplexed, 51 * non-blocking <br> I/O</a> facility. </p></li> 52 * 53 * </ul> 54 * 55 * <p> The {@code java.nio} package defines the buffer classes, which 56 * are used throughout the NIO APIs. The charset API is defined in 57 * the {@link java.nio.charset} package, and the channel and selector 58 * APIs are defined in the {@link java.nio.channels} package. Each of 59 * these subpackages has its own service-provider (SPI) subpackage, 60 * the contents of which can be used to extend the platform's default 61 * implementations or to construct alternative implementations. 62 * 63 * <a id="buffers"> </a> 64 * 65 * <table class="striped" style="margin-left:2em; text-align:left"> 66 * <caption style="display:none">Description of the various buffers</caption> 67 * <thead> 68 * <tr><th scope="col">Buffers</th> 69 * <th scope="col">Description</th></tr> 70 * </thead> 71 * <tbody> 72 * <tr><th scope="row">{@link java.nio.Buffer}</th> 73 * <td>Position, limit, and capacity; 74 * clear, flip, rewind, and mark/reset</td></tr> 75 * <tr><th scope="row"> 76 * <span style="padding-left:1em">{@link java.nio.ByteBuffer}</span></th> 77 * <td>Get/put, compact, views; allocate, wrap</td></tr> 78 * <tr><th scope="row"> 79 * <span style="padding-left:2em">{@link java.nio.MappedByteBuffer}</span></th> 80 * <td>A byte buffer mapped to a file</td></tr> 81 * <tr><th scope="row"> 82 * <span style="padding-left:1em">{@link java.nio.CharBuffer}</span></th> 83 * <td>Get/put, compact; allocate, wrap</td></tr> 84 * <tr><th scope="row"> 85 * <span style="padding-left:1em">{@link java.nio.DoubleBuffer}</span></th> 86 * <td>Get/put, compact; allocate, wrap</td></tr> 87 * <tr><th scope="row"> 88 * <span style="padding-left:1em">{@link java.nio.FloatBuffer}</span></th> 89 * <td>Get/put, compact; allocate, wrap</td></tr> 90 * <tr><th scope="row"> 91 * <span style="padding-left:1em">{@link java.nio.IntBuffer}</span></th> 92 * <td>Get/put, compact; allocate, wrap</td></tr> 93 * <tr><th scope="row"> 94 * <span style="padding-left:1em">{@link java.nio.LongBuffer}</span></th> 95 * <td>Get/put, compact; allocate, wrap</td></tr> 96 * <tr><th scope="row"> 97 * <span style="padding-left:1em">{@link java.nio.ShortBuffer}</span></th> 98 * <td>Get/put, compact; allocate, wrap</td></tr> 99 * <tr><th scope="row">{@link java.nio.ByteOrder}</th> 100 * <td>Typesafe enumeration for byte orders</td></tr> 101 * </tbody> 102 * </table> 103 * 104 * <p> A <i>buffer</i> is a container for a fixed amount of data of a 105 * specific primitive type. In addition to its content a buffer has a 106 * <i>position</i>, which is the index of the next element to be read 107 * or written, and a <i>limit</i>, which is the index of the first 108 * element that should not be read or written. The base {@link 109 * java.nio.Buffer} class defines these properties as well as methods 110 * for <i>clearing</i>, <i>flipping</i>, and <i>rewinding</i>, for 111 * <i>marking</i> the current position, and for <i>resetting</i> the 112 * position to the previous mark. 113 * 114 * <p> There is a buffer class for each non-boolean primitive type. 115 * Each class defines a family of <i>get</i> and <i>put</i> methods 116 * for moving data out of and in to a buffer, methods for 117 * <i>compacting</i>, <i>duplicating</i>, and <i>slicing</i> a buffer, 118 * and static methods for <i>allocating</i> a new buffer as well as 119 * for <i>wrapping</i> an existing array into a buffer. 120 * 121 * <p> Byte buffers are distinguished in that they can be used as the 122 * sources and targets of I/O operations. They also support several 123 * features not found in the other buffer classes: 124 * 125 * <ul> 126 * 127 * <li><p> A byte buffer can be allocated as a <a 128 * href="ByteBuffer.html#direct"> <i>direct</i></a> buffer, in which 129 * case the Java virtual machine will make a best effort to perform 130 * native I/O operations directly upon it. </p></li> 131 * 132 * <li><p> A byte buffer can be created by {@link 133 * java.nio.channels.FileChannel#map <i>mapping</i>} a region of a 134 * file directly into memory, in which case a few additional 135 * file-related operations defined in the {@link 136 * java.nio.MappedByteBuffer} class are available. </p></li> 137 * 138 * <li><p> A byte buffer provides access to its content as either a 139 * heterogeneous or homogeneous sequence of <a 140 * href="ByteBuffer.html#bin"><i>binary data</i></a> of any 141 * non-boolean primitive type, in either big-endian or little-endian 142 * <a href="ByteOrder.html">byte order</a>. </p></li> 143 * 144 * </ul> 145 * 146 * <p> Unless otherwise noted, passing a {@code null} argument to a 147 * constructor or method in any class or interface in this package 148 * will cause a {@link java.lang.NullPointerException 149 * NullPointerException} to be thrown. 150 * 151 * @since 1.4 152 * @author Mark Reinhold 153 * @author JSR-51 Expert Group 154 */ 155 package java.nio; 156