code: public String replaceText(String originalStr, String oldStr,
              String newStr) {
          if (oldStr == null || newStr == null || oldStr.equals(newStr)) {
              return originalStr;
          }
          return originalStr.replace(oldStr, newStr);
      }
docs: Given a string, replace all occurrences of 'newStr' with 'oldStr'.
  @param originalStr the string to modify.
  @param oldStr the string to replace.
  @param newStr the string to insert in place of the old string.