protected void createCompactor(Configuration conf, HStore store) throws IOException {
    String className = conf.get(DEFAULT_COMPACTOR_CLASS_KEY, DEFAULT_COMPACTOR_CLASS.getName());
    try {
      compactor = ReflectionUtils.instantiateWithCustomCtor(className,
        new Class[] { Configuration.class, HStore.class }, new Object[] { conf, store });
    } catch (Exception e) {
      throw new IOException("Unable to load configured compactor '" + className + "'", e);
    }
  }
Default StoreEngine creates the default compactor, policy, and store file manager, or their
derivatives.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/DefaultStoreEngine.java