code: public void setMonetaryDecimalSeparatorString(String sep) {
          if (sep == null) {
              throw new NullPointerException("The input monetary decimal separator is null");
          }
          this.monetarySeparatorString = sep;
          if (sep.length() == 1) {
              this.monetarySeparator = sep.charAt(0);
          } else {
              // Use default decimap separator character as fallbacl
              this.monetarySeparator = DEF_DECIMAL_SEPARATOR;
          }
      }
docs: <strong>[icu]</strong> Sets the monetary decimal separator string.
  <p>
  <b>Note:</b> When the input monetary decimal separator String is represented
  by multiple Java chars, then {@link #getMonetaryDecimalSeparatorString()} will
  return the default monetary decimal separator character ('.').
  
  @param sep the monetary decimal separator string
  @throws NullPointerException if <code>sep</code> is null.
  @see #getMonetaryDecimalSeparatorString()
  @hide draft / provisional / internal are hidden on Android