@Override
  public <U> Class<? extends U> getClass(String name, Class<? extends U> defaultValue,
    Class<U> xface) {
    return conf.getClass(name, defaultValue, xface);
  }
Wraps a Configuration to make it read-only.
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/ReadOnlyConfiguration.java