1/*
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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
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7 * published by the Free Software Foundation.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
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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).
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24 */
25
26package java.nio.channels;
27
28import java.nio.ByteBuffer;
29import java.io.IOException;
30
31/**
32 * A byte channel that maintains a current <i>position</i> and allows the
33 * position to be changed.
34 *
35 * <p> A seekable byte channel is connected to an entity, typically a file,
36 * that contains a variable-length sequence of bytes that can be read and
37 * written. The current position can be {@link #position() <i>queried</i>} and
38 * {@link #position(long) <i>modified</i>}. The channel also provides access to
39 * the current <i>size</i> of the entity to which the channel is connected. The
40 * size increases when bytes are written beyond its current size; the size
41 * decreases when it is {@link #truncate <i>truncated</i>}.
42 *
43 * <p> The {@link #position(long) position} and {@link #truncate truncate} methods
44 * which do not otherwise have a value to return are specified to return the
45 * channel upon which they are invoked. This allows method invocations to be
46 * chained. Implementations of this interface should specialize the return type
47 * so that method invocations on the implementation class can be chained.
48 *
49 * @since 1.7
50 * @see java.nio.file.Files#newByteChannel
51 */
52
53public interface SeekableByteChannel
54    extends ByteChannel
55{
56    /**
57     * Reads a sequence of bytes from this channel into the given buffer.
58     *
59     * <p> Bytes are read starting at this channel's current position, and
60     * then the position is updated with the number of bytes actually read.
61     * Otherwise this method behaves exactly as specified in the {@link
62     * ReadableByteChannel} interface.
63     */
64    @Override
65    int read(ByteBuffer dst) throws IOException;
66
67    /**
68     * Writes a sequence of bytes to this channel from the given buffer.
69     *
70     * <p> Bytes are written starting at this channel's current position, unless
71     * the channel is connected to an entity such as a file that is opened with
72     * the {@link java.nio.file.StandardOpenOption#APPEND APPEND} option, in
73     * which case the position is first advanced to the end. The entity to which
74     * the channel is connected is grown, if necessary, to accommodate the
75     * written bytes, and then the position is updated with the number of bytes
76     * actually written. Otherwise this method behaves exactly as specified by
77     * the {@link WritableByteChannel} interface.
78     */
79    @Override
80    int write(ByteBuffer src) throws IOException;
81
82    /**
83     * Returns this channel's position.
84     *
85     * @return  This channel's position,
86     *          a non-negative integer counting the number of bytes
87     *          from the beginning of the entity to the current position
88     *
89     * @throws  ClosedChannelException
90     *          If this channel is closed
91     * @throws  IOException
92     *          If some other I/O error occurs
93     */
94    long position() throws IOException;
95
96    /**
97     * Sets this channel's position.
98     *
99     * <p> Setting the position to a value that is greater than the current size
100     * is legal but does not change the size of the entity.  A later attempt to
101     * read bytes at such a position will immediately return an end-of-file
102     * indication.  A later attempt to write bytes at such a position will cause
103     * the entity to grow to accommodate the new bytes; the values of any bytes
104     * between the previous end-of-file and the newly-written bytes are
105     * unspecified.
106     *
107     * <p> Setting the channel's position is not recommended when connected to
108     * an entity, typically a file, that is opened with the {@link
109     * java.nio.file.StandardOpenOption#APPEND APPEND} option. When opened for
110     * append, the position is first advanced to the end before writing.
111     *
112     * @param  newPosition
113     *         The new position, a non-negative integer counting
114     *         the number of bytes from the beginning of the entity
115     *
116     * @return  This channel
117     *
118     * @throws  ClosedChannelException
119     *          If this channel is closed
120     * @throws  IllegalArgumentException
121     *          If the new position is negative
122     * @throws  IOException
123     *          If some other I/O error occurs
124     */
125    SeekableByteChannel position(long newPosition) throws IOException;
126
127    /**
128     * Returns the current size of entity to which this channel is connected.
129     *
130     * @return  The current size, measured in bytes
131     *
132     * @throws  ClosedChannelException
133     *          If this channel is closed
134     * @throws  IOException
135     *          If some other I/O error occurs
136     */
137    long size() throws IOException;
138
139    /**
140     * Truncates the entity, to which this channel is connected, to the given
141     * size.
142     *
143     * <p> If the given size is less than the current size then the entity is
144     * truncated, discarding any bytes beyond the new end. If the given size is
145     * greater than or equal to the current size then the entity is not modified.
146     * In either case, if the current position is greater than the given size
147     * then it is set to that size.
148     *
149     * <p> An implementation of this interface may prohibit truncation when
150     * connected to an entity, typically a file, opened with the {@link
151     * java.nio.file.StandardOpenOption#APPEND APPEND} option.
152     *
153     * @param  size
154     *         The new size, a non-negative byte count
155     *
156     * @return  This channel
157     *
158     * @throws  NonWritableChannelException
159     *          If this channel was not opened for writing
160     * @throws  ClosedChannelException
161     *          If this channel is closed
162     * @throws  IllegalArgumentException
163     *          If the new size is negative
164     * @throws  IOException
165     *          If some other I/O error occurs
166     */
167    SeekableByteChannel truncate(long size) throws IOException;
168}
169