gistfile1.java

Reflections reflections = new Reflections("pl.edu.polsl.labjava");

commandMap = new TreeMap<String, Class<? extends Command>>();

Set<Class<? extends Command>> commandClasses = reflections.getSubTypesOf(Command.class);

commandClasses.stream()
              .map((Function<Class<? extends Command>, KeyValue<String, Class<? extends Command>>>) (commandClass -> {
                  String commandName;
                  try {
                      commandName = (String) commandClass.getField("COMMAND_NAME").get(null);
                  } catch (IllegalAccessException | NoSuchFieldException e) {
                      System.err.format("Class \"%s\" does not hace a COMMAND_NAME field. Skipping.", commandClass);
                      return null;
                  }
                  return new KeyValue<>(commandName, commandClass);
              }))
              .filter(pair -> pair != null)
              .forEachOrdered(pair -> commandMap.put(pair.getKey(), pair.getValue()));