The rarest-first sort is stable, so randomize the wantedPieces list to ensure a healthy swarm when you have mostly seeders.

apps/i2psnark/java/src/org/klomp/snark/PeerCoordinator.java

@@ -75,6 +75,7 @@ public class PeerCoordinator implements PeerListener
     for(int i = 0; i < metainfo.getPieces(); i++)
       if (!bitfield.get(i))
         wantedPieces.add(new Piece(i));
+    Collections.shuffle(wantedPieces);
 
     // Install a timer to check the uploaders.
     timer.schedule(new PeerCheckerTask(this), CHECK_PERIOD, CHECK_PERIOD);

apps/i2psnark/java/src/org/klomp/snark/Piece.java

@@ -12,6 +12,7 @@ public class Piece implements Comparable {
     public Piece(int id) {
         this.id = id;
         this.peers = new HashSet();
+        this.requested = false;
     }
     
     public int compareTo(Object o) throws ClassCastException {