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1   /*
2    * Copyright 2019 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   https://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.resolver.dns;
17  
18  import io.netty.channel.socket.SocketProtocolFamily;
19  
20  import java.net.Inet4Address;
21  import java.net.Inet6Address;
22  import java.net.InetAddress;
23  import java.util.Comparator;
24  
25  final class PreferredAddressTypeComparator implements Comparator<InetAddress> {
26  
27      private static final PreferredAddressTypeComparator IPv4 = new PreferredAddressTypeComparator(Inet4Address.class);
28      private static final PreferredAddressTypeComparator IPv6 = new PreferredAddressTypeComparator(Inet6Address.class);
29  
30      static PreferredAddressTypeComparator comparator(SocketProtocolFamily family) {
31          switch (family) {
32              case INET:
33                  return IPv4;
34              case INET6:
35                  return IPv6;
36              default:
37                  throw new IllegalArgumentException();
38          }
39      }
40  
41      private final Class<? extends InetAddress> preferredAddressType;
42  
43      private PreferredAddressTypeComparator(Class<? extends InetAddress> preferredAddressType) {
44          this.preferredAddressType = preferredAddressType;
45      }
46  
47      @Override
48      public int compare(InetAddress o1, InetAddress o2) {
49          if (o1.getClass() == o2.getClass()) {
50              return 0;
51          }
52          return preferredAddressType.isAssignableFrom(o1.getClass()) ? -1 : 1;
53      }
54  }