code: public static boolean isAllLowerCase(String str) {
          if (str == null || isEmpty(str)) {
              return false;
          }
          int sz = str.length();
          for (int i = 0; i < sz; i++) {
              if (Character.isLowerCase(str.charAt(i)) == false) {
                  return false;
              }
          }
          return true;
      }
docs: <p>Checks if the String contains only lowercase characters.</p>
  
  <p><code>null</code> will return <code>false</code>.
  An empty String (length()=0) will return <code>false</code>.</p>
  
  <pre>
  StringUtils.isAllLowerCase(null)   = false
  StringUtils.isAllLowerCase("")     = false
  StringUtils.isAllLowerCase("  ")   = false
  StringUtils.isAllLowerCase("abc")  = true
  StringUtils.isAllLowerCase("abC") = false
  </pre>
  
  @param str  the String to check, may be null
  @return <code>true</code> if only contains lowercase characters, and is non-null
  @since 2.5