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25 
26 package java.nio.channels;
27 
28 import java.io.IOException;
29 import java.nio.ByteBuffer;
30 
31 
32 /**
33  * A channel that can read bytes.
34  *
35  * <p> Only one read operation upon a readable channel may be in progress at
36  * any given time.  If one thread initiates a read operation upon a channel
37  * then any other thread that attempts to initiate another read operation will
38  * block until the first operation is complete.  Whether or not other kinds of
39  * I/O operations may proceed concurrently with a read operation depends upon
40  * the type of the channel. </p>
41  *
42  *
43  * @author Mark Reinhold
44  * @author JSR-51 Expert Group
45  * @since 1.4
46  */
47 
48 public interface ReadableByteChannel extends Channel {
49 
50     /**
51      * Reads a sequence of bytes from this channel into the given buffer.
52      *
53      * <p> An attempt is made to read up to <i>r</i> bytes from the channel,
54      * where <i>r</i> is the number of bytes remaining in the buffer, that is,
55      * <tt>dst.remaining()</tt>, at the moment this method is invoked.
56      *
57      * <p> Suppose that a byte sequence of length <i>n</i> is read, where
58      * <tt>0</tt>&nbsp;<tt>&lt;=</tt>&nbsp;<i>n</i>&nbsp;<tt>&lt;=</tt>&nbsp;<i>r</i>.
59      * This byte sequence will be transferred into the buffer so that the first
60      * byte in the sequence is at index <i>p</i> and the last byte is at index
61      * <i>p</i>&nbsp;<tt>+</tt>&nbsp;<i>n</i>&nbsp;<tt>-</tt>&nbsp;<tt>1</tt>,
62      * where <i>p</i> is the buffer's position at the moment this method is
63      * invoked.  Upon return the buffer's position will be equal to
64      * <i>p</i>&nbsp;<tt>+</tt>&nbsp;<i>n</i>; its limit will not have changed.
65      *
66      * <p> A read operation might not fill the buffer, and in fact it might not
67      * read any bytes at all.  Whether or not it does so depends upon the
68      * nature and state of the channel.  A socket channel in non-blocking mode,
69      * for example, cannot read any more bytes than are immediately available
70      * from the socket's input buffer; similarly, a file channel cannot read
71      * any more bytes than remain in the file.  It is guaranteed, however, that
72      * if a channel is in blocking mode and there is at least one byte
73      * remaining in the buffer then this method will block until at least one
74      * byte is read.
75      *
76      * <p> This method may be invoked at any time.  If another thread has
77      * already initiated a read operation upon this channel, however, then an
78      * invocation of this method will block until the first operation is
79      * complete. </p>
80      *
81      * @param  dst
82      *         The buffer into which bytes are to be transferred
83      *
84      * @return  The number of bytes read, possibly zero, or <tt>-1</tt> if the
85      *          channel has reached end-of-stream
86      *
87      * @throws  NonReadableChannelException
88      *          If this channel was not opened for reading
89      *
90      * @throws  ClosedChannelException
91      *          If this channel is closed
92      *
93      * @throws  AsynchronousCloseException
94      *          If another thread closes this channel
95      *          while the read operation is in progress
96      *
97      * @throws  ClosedByInterruptException
98      *          If another thread interrupts the current thread
99      *          while the read operation is in progress, thereby
100      *          closing the channel and setting the current thread's
101      *          interrupt status
102      *
103      * @throws  IOException
104      *          If some other I/O error occurs
105      */
read(ByteBuffer dst)106     public int read(ByteBuffer dst) throws IOException;
107 
108 }
109