code: public static void replaceMultipleTo (@Nullable final String sInputString,
                                          @Nonnull final char [] aSearchChars,
                                          final char cReplacementChar,
                                          @Nonnull final Writer aTarget) throws IOException
    {
      ValueEnforcer.notNull (aSearchChars, "SearchChars");
      ValueEnforcer.notNull (aTarget, "Target");
  
      // Any input text?
      if (hasText (sInputString))
      {
        // Any search chars?
        if (aSearchChars.length == 0)
        {
          aTarget.write (sInputString);
        }
        else
        {
          // Perform the replacement
          for (final char c : sInputString.toCharArray ())
          {
            if (ArrayHelper.contains (aSearchChars, c))
              aTarget.write (cReplacementChar);
            else
              aTarget.write (c);
          }
        }
      }
    }
docs: Optimized replace method that replaces a set of characters with another
  character. This method was created for efficient unsafe character
  replacements!
  
  @param sInputString
  The input string.
  @param aSearchChars
  The characters to replace.
  @param cReplacementChar
  The new char to be used instead of the search chars.
  @param aTarget
  The target writer to write the result to. May not be
  <code>null</code>.
  @throws IOException
  in case writing to the Writer fails
  @since 8.6.3