code: public static String firstCharToLowerCase(String str) {
  		char firstChar = str.charAt(0);
  		if (firstChar >= 'A' && firstChar <= 'Z') {
  			char[] arr = str.toCharArray();
  			arr[0] += ('a' - 'A');
  			return new String(arr);
  		}
  		return str;
  	}
docs: 首字母变小写