code: @Override
  	public Set<String> getPrefixes() {
  		lock.readLock().lock();
  		try {
  			return new TreeSet<String>(prefixes);
  		} finally {
  			lock.readLock().unlock();
  		}
  	}
docs: /*
  (non-Javadoc)
  
  @see net.sf.prefixedproperties.config.PrefixConfig#getPrefixes()