大文字転下線のアルゴリズムアルパカ転下線

public static String camel4underline(String param){
		Pattern  p=Pattern.compile("[A-Z]");
		if(param==null ||param.equals("")){
			return "";
		}
		StringBuilder builder=new StringBuilder(param);
		Matcher mc=p.matcher(param);
		int i=0;
		while(mc.find()){
			builder.replace(mc.start()+i, mc.end()+i, "_"+mc.group().toLowerCase());
			i++;
		}

		if('_' == builder.charAt(0)){
			builder.deleteCharAt(0);
		}
		return builder.toString();
	}