/* * Copyright (c) 2007, 2009, 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.net.InetAddress;import java.net.NetworkInterface;import java.io.IOException; /** * A token representing the membership of an Internet Protocol (IP) multicast * group. * * <p> A membership key may represent a membership to receive all datagrams sent * to the group, or it may be <em>source-specific</em>, meaning that it * represents a membership that receives only datagrams from a specific source * address. Whether or not a membership key is source-specific may be determined * by invoking its {@link #sourceAddress() sourceAddress} method. * * <p> A membership key is valid upon creation and remains valid until the * membership is dropped by invoking the {@link #drop() drop} method, or * the channel is closed. The validity of the membership key may be tested * by invoking its {@link #isValid() isValid} method. * * <p> Where a membership key is not source-specific and the underlying operation * system supports source filtering, then the {@link #block block} and {@link * #unblock unblock} methods can be used to block or unblock multicast datagrams * from particular source addresses. * * @see MulticastChannel * * @since 1.7 */public abstract class MembershipKey {     /**     * Initializes a new instance of this class.     */    protected MembershipKey() {    }     /**     * Tells whether or not this membership is valid.     *     * <p> A multicast group membership is valid upon creation and remains     * valid until the membership is dropped by invoking the {@link #drop() drop}     * method, or the channel is closed.     *     * @return  {@code true} if this membership key is valid, {@code false}     *          otherwise     */    public abstract boolean isValid();     /**     * Drop membership.     *     * <p> If the membership key represents a membership to receive all datagrams     * then the membership is dropped and the channel will no longer receive any     * datagrams sent to the group. If the membership key is source-specific     * then the channel will no longer receive datagrams sent to the group from     * that source address.     *     * <p> After membership is dropped it may still be possible to receive     * datagrams sent to the group. This can arise when datagrams are waiting to     * be received in the socket's receive buffer. After membership is dropped     * then the channel may {@link MulticastChannel#join join} the group again     * in which case a new membership key is returned.     *     * <p> Upon return, this membership object will be {@link #isValid() invalid}.     * If the multicast group membership is already invalid then invoking this     * method has no effect. Once a multicast group membership is invalid,     * it remains invalid forever.     */    public abstract void drop();     /**     * Block multicast datagrams from the given source address.     *     * <p> If this membership key is not source-specific, and the underlying     * operating system supports source filtering, then this method blocks     * multicast datagrams from the given source address. If the given source     * address is already blocked then this method has no effect.     * After a source address is blocked it may still be possible to receive     * datagams from that source. This can arise when datagrams are waiting to     * be received in the socket's receive buffer.     *     * @param   source     *          The source address to block     *     * @return  This membership key     *     * @throws  IllegalArgumentException     *          If the {@code source} parameter is not a unicast address or     *          is not the same address type as the multicast group     * @throws  IllegalStateException     *          If this membership key is source-specific or is no longer valid     * @throws  UnsupportedOperationException     *          If the underlying operating system does not support source     *          filtering     * @throws  IOException     *          If an I/O error occurs     */    public abstract MembershipKey block(InetAddress source) throws IOException;     /**     * Unblock multicast datagrams from the given source address that was     * previously blocked using the {@link #block(InetAddress) block} method.     *     * @param   source     *          The source address to unblock     *     * @return  This membership key     *     * @throws  IllegalStateException     *          If the given source address is not currently blocked or the     *          membership key is no longer valid     */    public abstract MembershipKey unblock(InetAddress source);     /**     * Returns the channel for which this membership key was created. This     * method will continue to return the channel even after the membership     * becomes {@link #isValid invalid}.     *     * @return  the channel     */    public abstract MulticastChannel channel();     /**     * Returns the multicast group for which this membership key was created.     * This method will continue to return the group even after the membership     * becomes {@link #isValid invalid}.     *     * @return  the multicast group     */    public abstract InetAddress group();     /**     * Returns the network interface for which this membership key was created.     * This method will continue to return the network interface even after the     * membership becomes {@link #isValid invalid}.     *     * @return  the network interface     */    public abstract NetworkInterface networkInterface();     /**     * Returns the source address if this membership key is source-specific,     * or {@code null} if this membership is not source-specific.     *     * @return  The source address if this membership key is source-specific,     *          otherwise {@code null}     */    public abstract InetAddress sourceAddress();}