code: @Override
      public final boolean isSecure(Socket sock)
              throws IllegalArgumentException {
  
          if (sock == null) {
              throw new IllegalArgumentException("Socket may not be null.");
          }
          // This check is performed last since it calls a method implemented
          // by the argument object. getClass() is final in java.lang.Object.
          if (sock.isClosed()) {
              throw new IllegalArgumentException("Socket is closed.");
          }
          return false;
      }
docs: Checks whether a socket connection is secure. This factory creates plain socket connections which are not
  considered secure.
  
  @param sock the connected socket
  @return <code>false</code>
  @throws IllegalArgumentException if the argument is invalid