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 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

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package java.nio.channels;

import java.nio.ByteBuffer;

import java.io.IOException;

/**

 * A byte channel that maintains a current <i>position</i> and allows the

 * position to be changed.

 *

 * <p> A seekable byte channel is connected to an entity, typically a file,

 * that contains a variable-length sequence of bytes that can be read and

 * written. The current position can be {@link #position() <i>queried</i>} and

 * {@link #position(long) <i>modified</i>}. The channel also provides access to

 * the current <i>size</i> of the entity to which the channel is connected. The

 * size increases when bytes are written beyond its current size; the size

 * decreases when it is {@link #truncate <i>truncated</i>}.

 *

 * <p> The {@link #position(long) position} and {@link #truncate truncate} methods

 * which do not otherwise have a value to return are specified to return the

 * channel upon which they are invoked. This allows method invocations to be

 * chained. Implementations of this interface should specialize the return type

 * so that method invocations on the implementation class can be chained.

 *

 * @since 1.7

 * @see java.nio.file.Files#newByteChannel

 */

public interface SeekableByteChannel

    extends ByteChannel

{

    /**

     * Reads a sequence of bytes from this channel into the given buffer.

     *

     * <p> Bytes are read starting at this channel's current position, and

     * then the position is updated with the number of bytes actually read.

     * Otherwise this method behaves exactly as specified in the {@link

     * ReadableByteChannel} interface.

     */

    @Override

    int read(ByteBuffer dst) throws IOException;

    /**

     * Writes a sequence of bytes to this channel from the given buffer.

     *

     * <p> Bytes are written starting at this channel's current position, unless

     * the channel is connected to an entity such as a file that is opened with

     * the {@link java.nio.file.StandardOpenOption#APPEND APPEND} option, in

     * which case the position is first advanced to the end. The entity to which

     * the channel is connected is grown, if necessary, to accommodate the

     * written bytes, and then the position is updated with the number of bytes

     * actually written. Otherwise this method behaves exactly as specified by

     * the {@link WritableByteChannel} interface.

     */

    @Override

    int write(ByteBuffer src) throws IOException;

    /**

     * Returns this channel's position.

     *

     * @return  This channel's position,

     *          a non-negative integer counting the number of bytes

     *          from the beginning of the entity to the current position

     *

     * @throws  ClosedChannelException

     *          If this channel is closed

     * @throws  IOException

     *          If some other I/O error occurs

     */

    long position() throws IOException;

    /**

     * Sets this channel's position.

     *

     * <p> Setting the position to a value that is greater than the current size

     * is legal but does not change the size of the entity.  A later attempt to

     * read bytes at such a position will immediately return an end-of-file

     * indication.  A later attempt to write bytes at such a position will cause

     * the entity to grow to accommodate the new bytes; the values of any bytes

     * between the previous end-of-file and the newly-written bytes are

     * unspecified.

     *

     * <p> Setting the channel's position is not recommended when connected to

     * an entity, typically a file, that is opened with the {@link

     * java.nio.file.StandardOpenOption#APPEND APPEND} option. When opened for

     * append, the position is first advanced to the end before writing.

     *

     * @param  newPosition

     *         The new position, a non-negative integer counting

     *         the number of bytes from the beginning of the entity

     *

     * @return  This channel

     *

     * @throws  ClosedChannelException

     *          If this channel is closed

     * @throws  IllegalArgumentException

     *          If the new position is negative

     * @throws  IOException

     *          If some other I/O error occurs

     */

    SeekableByteChannel position(long newPosition) throws IOException;

    /**

     * Returns the current size of entity to which this channel is connected.

     *

     * @return  The current size, measured in bytes

     *

     * @throws  ClosedChannelException

     *          If this channel is closed

     * @throws  IOException

     *          If some other I/O error occurs

     */

    long size() throws IOException;

    /**

     * Truncates the entity, to which this channel is connected, to the given

     * size.

     *

     * <p> If the given size is less than the current size then the entity is

     * truncated, discarding any bytes beyond the new end. If the given size is

     * greater than or equal to the current size then the entity is not modified.

     * In either case, if the current position is greater than the given size

     * then it is set to that size.

     *

     * <p> An implementation of this interface may prohibit truncation when

     * connected to an entity, typically a file, opened with the {@link

     * java.nio.file.StandardOpenOption#APPEND APPEND} option.

     *

     * @param  size

     *         The new size, a non-negative byte count

     *

     * @return  This channel

     *

     * @throws  NonWritableChannelException

     *          If this channel was not opened for writing

     * @throws  ClosedChannelException

     *          If this channel is closed

     * @throws  IllegalArgumentException

     *          If the new size is negative

     * @throws  IOException

     *          If some other I/O error occurs

     */

    SeekableByteChannel truncate(long size) throws IOException;

}