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package java.nio.channels;

import java.io.IOException;
import java.nio.ByteBuffer;



A channel that can read bytes.

 Only one read operation upon a readable channel may be in progress at
any given time.  If one thread initiates a read operation upon a channel
then any other thread that attempts to initiate another read operation will
block until the first operation is complete.  Whether or not other kinds of
I/O operations may proceed concurrently with a read operation depends upon
the type of the channel. 


Author:Mark Reinhold, JSR-51 Expert Group
Since:1.4
/**
 * A channel that can read bytes.
 *
 * <p> Only one read operation upon a readable channel may be in progress at
 * any given time.  If one thread initiates a read operation upon a channel
 * then any other thread that attempts to initiate another read operation will
 * block until the first operation is complete.  Whether or not other kinds of
 * I/O operations may proceed concurrently with a read operation depends upon
 * the type of the channel. </p>
 *
 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 */

public interface ReadableByteChannel extends Channel {

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

 An attempt is made to read up to r bytes from the channel,
where r is the number of bytes remaining in the buffer, that is, dst.remaining(), at the moment this method is invoked. 
 Suppose that a byte sequence of length n is read, where 0 <= n <= r.
This byte sequence will be transferred into the buffer so that the first
byte in the sequence is at index p and the last byte is at index
p + n - 1, where p is the buffer's position at the moment this method is
invoked.  Upon return the buffer's position will be equal to
p + n; its limit will not have changed.

 A read operation might not fill the buffer, and in fact it might not
read any bytes at all.  Whether or not it does so depends upon the
nature and state of the channel.  A socket channel in non-blocking mode,
for example, cannot read any more bytes than are immediately available
from the socket's input buffer; similarly, a file channel cannot read
any more bytes than remain in the file.  It is guaranteed, however, that
if a channel is in blocking mode and there is at least one byte
remaining in the buffer then this method will block until at least one
byte is read.

 This method may be invoked at any time.  If another thread has
already initiated a read operation upon this channel, however, then an
invocation of this method will block until the first operation is
complete. 


Params:
  • dst – 
        The buffer into which bytes are to be transferred
Throws:
Returns: The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream
/**
     * Reads a sequence of bytes from this channel into the given buffer.
     *
     * <p> An attempt is made to read up to <i>r</i> bytes from the channel,
     * where <i>r</i> is the number of bytes remaining in the buffer, that is,
     * {@code dst.remaining()}, at the moment this method is invoked.
     *
     * <p> Suppose that a byte sequence of length <i>n</i> is read, where
     * {@code 0}&nbsp;{@code <=}&nbsp;<i>n</i>&nbsp;{@code <=}&nbsp;<i>r</i>.
     * This byte sequence will be transferred into the buffer so that the first
     * byte in the sequence is at index <i>p</i> and the last byte is at index
     * <i>p</i>&nbsp;{@code +}&nbsp;<i>n</i>&nbsp;{@code -}&nbsp;{@code 1},
     * where <i>p</i> is the buffer's position at the moment this method is
     * invoked.  Upon return the buffer's position will be equal to
     * <i>p</i>&nbsp;{@code +}&nbsp;<i>n</i>; its limit will not have changed.
     *
     * <p> A read operation might not fill the buffer, and in fact it might not
     * read any bytes at all.  Whether or not it does so depends upon the
     * nature and state of the channel.  A socket channel in non-blocking mode,
     * for example, cannot read any more bytes than are immediately available
     * from the socket's input buffer; similarly, a file channel cannot read
     * any more bytes than remain in the file.  It is guaranteed, however, that
     * if a channel is in blocking mode and there is at least one byte
     * remaining in the buffer then this method will block until at least one
     * byte is read.
     *
     * <p> This method may be invoked at any time.  If another thread has
     * already initiated a read operation upon this channel, however, then an
     * invocation of this method will block until the first operation is
     * complete. </p>
     *
     * @param  dst
     *         The buffer into which bytes are to be transferred
     *
     * @return  The number of bytes read, possibly zero, or {@code -1} if the
     *          channel has reached end-of-stream
     *
     * @throws  IllegalArgumentException
     *          If the buffer is read-only
     *
     * @throws  NonReadableChannelException
     *          If this channel was not opened for reading
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  AsynchronousCloseException
     *          If another thread closes this channel
     *          while the read operation is in progress
     *
     * @throws  ClosedByInterruptException
     *          If another thread interrupts the current thread
     *          while the read operation is in progress, thereby
     *          closing the channel and setting the current thread's
     *          interrupt status
     *
     * @throws  IOException
     *          If some other I/O error occurs
     */
    public int read(ByteBuffer dst) throws IOException;

}