code: public boolean checkEquals(String str1, String str2) {
          if ((str1 == null) || (str2 == null)) {
              throw new NullPointerException("The strings must not be null");
          }
          return isSensitive ? str1.equals(str2) : str1.equalsIgnoreCase(str2);
      }
docs: Compares two strings using the case-sensitivity rule.
  <p>
  This method mimics {@link String#equals} but takes case-sensitivity
  into account.
  
  @param str1  the first string to compare, not null
  @param str2  the second string to compare, not null
  @return true if equal using the case rules
  @throws NullPointerException if either string is null