docs: public static void main(String[] args) throws Exception {
  
          if (args.length < 2 || args.length == 4 || args.length > 5) {
              System.out.println("USAGE: HelloWorldClientTls host port [trustCertCollectionFilePath] " +
                      "[clientCertChainFilePath clientPrivateKeyFilePath]\n  Note: clientCertChainFilePath and " +
                      "clientPrivateKeyFilePath are only needed if mutual auth is desired.");
              System.exit(0);
          }
  
          HelloWorldClientTls client;
          switch (args.length) {
              case 2:
                  client = new HelloWorldClientTls(args[0], Integer.parseInt(args[1]),
                          buildSslContext(null, null, null));
                  break;
              case 3:
                  client = new HelloWorldClientTls(args[0], Integer.parseInt(args[1]),
                          buildSslContext(args[2], null, null));
                  break;
              default:
                  client = new HelloWorldClientTls(args[0], Integer.parseInt(args[1]),
                          buildSslContext(args[2], args[3], args[4]));
          }
  
          try {
              /* Access a service running on the local machine on port 50051 */
              String user = "world";
              if (args.length > 0) {
                  user = args[0]; /* Use the arg as the name to greet if provided */
              }
              client.greet(user);
          } finally {
              client.shutdown();
          }
      }