@Override
  public synchronized String toString() {
    // Display unified set of servers from both maps
    Set<ServerName> servers = new HashSet<>();
    servers.addAll(deadServers.keySet());
    StringBuilder sb = new StringBuilder();
    for (ServerName sn : servers) {
      if (sb.length() > 0) {
        sb.append(", ");
      }
      sb.append(sn.toString());
    }
    return sb.toString();
  }
@param newServerName      Server to match port and hostname against.
@param deadServerIterator Iterator primed so can call 'next' on it.
@return True if <code>newServerName</code> and current primed iterator ServerName have same
        host and port and we removed old server from iterator and from processing list.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/DeadServer.java