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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      */
MembershipKey()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      */
isValid()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      */
drop()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      */
block(InetAddress source)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      */
unblock(InetAddress source)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      */
channel()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      */
group()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      */
networkInterface()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      */
sourceAddress()176     public abstract InetAddress sourceAddress();
177 }
178