/* * Copyright (c) 2000, 2001, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * 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). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.nio.channels; import java.io.IOException;import java.nio.ByteBuffer;  /** * 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.     *     * <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,     * <tt>dst.remaining()</tt>, at the moment this method is invoked.     *     * <p> Suppose that a byte sequence of length <i>n</i> is read, where     * <tt>0</tt>&nbsp;<tt>&lt;=</tt>&nbsp;<i>n</i>&nbsp;<tt>&lt;=</tt>&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;<tt>+</tt>&nbsp;<i>n</i>&nbsp;<tt>-</tt>&nbsp;<tt>1</tt>,     * 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;<tt>+</tt>&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 <tt>-1</tt> if the     *          channel has reached end-of-stream     *     * @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; }