Class Pair<T1,T2>

java.lang.Object
com.frostwire.jlibtorrent.Pair<T1,T2>
Type Parameters:
T1 - the type of the first element
T2 - the type of the second element
public final class Pair<T1,T2> extends Object
Generic pair container for holding two related values of different types.

Pair mirrors the C++ std::pair template, providing a simple way to combine two heterogeneous values into a single object. This is commonly used in jlibtorrent for returning multiple values from methods and storing key-value pairs.

Understanding Pair Usage:
Pairs are used throughout jlibtorrent to represent:

  • Key-Value Pairs: Configuration settings, tracker/peer info
  • Coordinate Pairs: Range boundaries like (start, end)
  • Status Tuples: Combined result and status information
  • Native Interop: Mapping between Java and C++ pair types

Creating Pairs: 

 // String-String pair (e.g., name-value configuration)
 Pair<String, String> setting = new Pair<>(\"key\", \"value\");
 System.out.println(\"Key: \" + setting.first);
 System.out.println(\"Value: \" + setting.second);

 // String-Integer pair (e.g., name-port)
 Pair<String, Integer> endpoint = new Pair<>(\"example.com\", 6881);
 System.out.println(\"Host: \" + endpoint.first);
 System.out.println(\"Port: \" + endpoint.second);

 // Generic types
 Pair<Integer, Long> range = new Pair<>(0, 1024L);
 System.out.println(\"Start: \" + range.first);
 System.out.println(\"End: \" + range.second);

Using Pairs in Collections: 

 // Store multiple tracker/peer pairs
 java.util.List<Pair<String, Integer>> nodes =
     new java.util.ArrayList<>();

 nodes.add(new Pair<>(\"router.bittorrent.com\", 6881));
 nodes.add(new Pair<>(\"router.utorrent.com\", 6881));
 nodes.add(new Pair<>(\"dht.transmissionbt.com\", 6881));

 for (Pair<String, Integer> node : nodes) {
     System.out.println(\"Node: \" + node.first + \":\" + node.second);
 }

Native Conversion Methods:

Pair provides methods to convert between Java and native C++ pair types: 

 // Convert String-String pair to native type
 Pair<String, String> javaPair = new Pair<>(\"key\", \"value\");
 com.frostwire.jlibtorrent.swig.string_string_pair nativePair =
     javaPair.to_string_string_pair();

 // Convert String-Integer pair to native type
 Pair<String, Integer> config = new Pair<>(\"port\", 6881);
 com.frostwire.jlibtorrent.swig.string_int_pair nativeConfig =
     config.to_string_int_pair();

Common Use Cases in BitTorrent: 

 // DHT nodes (hostname:port pairs)
 Pair<String, Integer> dhtNode = new Pair<>(\"router.bittorrent.com\", 6881);

 // Trackers (url:tier pairs)
 Pair<String, Integer> tracker = new Pair<>(
     \"http://tracker.example.com/announce\",
     0  // tier 0 = primary
 );

 // Web seeds (url:priority pairs)
 Pair<String, Integer> webSeed = new Pair<>(
     \"http://example.com/torrent\",
     1  // priority
 );

Important Notes:

  • Pairs are immutable after creation (fields are final)
  • Both type parameters must be specified for type safety
  • Native conversion methods only support specific combinations (String-String, String-Integer)
  • Use diamond operator (<&gt;) for cleaner syntax in Java 7+
See Also:

  • Field Details

    • first

      public final T1 first
      the first element

    • second

      public final T2 second
      the second element

  • Constructor Details

    • Pair

      public Pair(T1 first, T2 second)
      Parameters:
      first - first element
      second - second element