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3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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9    * by Oracle in the LICENSE file that accompanied this code.
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11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
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17   * You should have received a copy of the GNU General Public License version
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25  
26  package java.nio.channels;
27  
28  import java.net.InetAddress;
29  import java.net.NetworkInterface;
30  import java.io.IOException;
31  
32  /**
33   * A token representing the membership of an Internet Protocol (IP) multicast
34   * group.
35   *
36   * <p> A membership key may represent a membership to receive all datagrams sent
37   * to the group, or it may be <em>source-specific</em>, meaning that it
38   * represents a membership that receives only datagrams from a specific source
39   * address. Whether or not a membership key is source-specific may be determined
40   * by invoking its {@link #sourceAddress() sourceAddress} method.
41   *
42   * <p> A membership key is valid upon creation and remains valid until the
43   * membership is dropped by invoking the {@link #drop() drop} method, or
44   * the channel is closed. The validity of the membership key may be tested
45   * by invoking its {@link #isValid() isValid} method.
46   *
47   * <p> Where a membership key is not source-specific and the underlying operation
48   * system supports source filtering, then the {@link #block block} and {@link
49   * #unblock unblock} methods can be used to block or unblock multicast datagrams
50   * from particular source addresses.
51   *
52   * @see MulticastChannel
53   *
54   * @since 1.7
55   */
56  public abstract class MembershipKey {
57  
58      /**
59       * Initializes a new instance of this class.
60       */
61      protected MembershipKey() {
62      }
63  
64      /**
65       * Tells whether or not this membership is valid.
66       *
67       * <p> A multicast group membership is valid upon creation and remains
68       * valid until the membership is dropped by invoking the {@link #drop() drop}
69       * method, or the channel is closed.
70       *
71       * @return  {@code true} if this membership key is valid, {@code false}
72       *          otherwise
73       */
74      public abstract boolean isValid();
75  
76      /**
77       * Drop membership.
78       *
79       * <p> If the membership key represents a membership to receive all datagrams
80       * then the membership is dropped and the channel will no longer receive any
81       * datagrams sent to the group. If the membership key is source-specific
82       * then the channel will no longer receive datagrams sent to the group from
83       * that source address.
84       *
85       * <p> After membership is dropped it may still be possible to receive
86       * datagrams sent to the group. This can arise when datagrams are waiting to
87       * be received in the socket's receive buffer. After membership is dropped
88       * then the channel may {@link MulticastChannel#join join} the group again
89       * in which case a new membership key is returned.
90       *
91       * <p> Upon return, this membership object will be {@link #isValid() invalid}.
92       * If the multicast group membership is already invalid then invoking this
93       * method has no effect. Once a multicast group membership is invalid,
94       * it remains invalid forever.
95       */
96      public abstract void drop();
97  
98      /**
99       * Block multicast datagrams from the given source address.
100      *
101      * <p> If this membership key is not source-specific, and the underlying
102      * operating system supports source filtering, then this method blocks
103      * multicast datagrams from the given source address. If the given source
104      * address is already blocked then this method has no effect.
105      * After a source address is blocked it may still be possible to receive
106      * datagrams from that source. This can arise when datagrams are waiting to
107      * be received in the socket's receive buffer.
108      *
109      * @param   source
110      *          The source address to block
111      *
112      * @return  This membership key
113      *
114      * @throws  IllegalArgumentException
115      *          If the {@code source} parameter is not a unicast address or
116      *          is not the same address type as the multicast group
117      * @throws  IllegalStateException
118      *          If this membership key is source-specific or is no longer valid
119      * @throws  UnsupportedOperationException
120      *          If the underlying operating system does not support source
121      *          filtering
122      * @throws  IOException
123      *          If an I/O error occurs
124      */
125     public abstract MembershipKey block(InetAddress source) throws IOException;
126 
127     /**
128      * Unblock multicast datagrams from the given source address that was
129      * previously blocked using the {@link #block(InetAddress) block} method.
130      *
131      * @param   source
132      *          The source address to unblock
133      *
134      * @return  This membership key
135      *
136      * @throws  IllegalStateException
137      *          If the given source address is not currently blocked or the
138      *          membership key is no longer valid
139      */
140     public abstract MembershipKey unblock(InetAddress source);
141 
142     /**
143      * Returns the channel for which this membership key was created. This
144      * method will continue to return the channel even after the membership
145      * becomes {@link #isValid invalid}.
146      *
147      * @return  the channel
148      */
149     public abstract MulticastChannel channel();
150 
151     /**
152      * Returns the multicast group for which this membership key was created.
153      * This method will continue to return the group even after the membership
154      * becomes {@link #isValid invalid}.
155      *
156      * @return  the multicast group
157      */
158     public abstract InetAddress group();
159 
160     /**
161      * Returns the network interface for which this membership key was created.
162      * This method will continue to return the network interface even after the
163      * membership becomes {@link #isValid invalid}.
164      *
165      * @return  the network interface
166      */
167     public abstract NetworkInterface networkInterface();
168 
169     /**
170      * Returns the source address if this membership key is source-specific,
171      * or {@code null} if this membership is not source-specific.
172      *
173      * @return  The source address if this membership key is source-specific,
174      *          otherwise {@code null}
175      */
176     public abstract InetAddress sourceAddress();
177 }