code: String decamelize(String str) {
  		StringBuilder builder = new StringBuilder();
  		int len = str.length();
  		for (int i = 0; i < len; i++) {
  			char c = str.charAt(i);
  			if ('A' <= c && c <= 'Z') {
  				builder.append('_').append(Character.toLowerCase(c));
  			} else {
  				builder.append(c);
  			}
  		}
  		return builder.toString();
  	}
docs: Decamelize string.<br>
  example, "fooBar" to "foo_bar".
  @param str
  @return decamelized string
  @author vvakame