code: public void collectUnfreshPeers(int expireTimeoutSec) {
      for (TrackedPeer peer : this.peers.values()) {
        if (!peer.isFresh(expireTimeoutSec)) {
          this.peers.remove(new PeerUID(peer.getAddress(), this.getHexInfoHash()));
        }
      }
    }
docs: Remove unfresh peers from this torrent.
  <p>
  <p>
  Collect and remove all non-fresh peers from this torrent. This is
  usually called by the periodic peer collector of the BitTorrent tracker.
  </p>