code: public static String valueOf(int char32) {
          if (char32 < CODEPOINT_MIN_VALUE || char32 > CODEPOINT_MAX_VALUE) {
              throw new IllegalArgumentException("Illegal codepoint");
          }
          return toString(char32);
      }
docs: Convenience method corresponding to String.valueOf(char). Returns a one or two char string
  containing the UTF-32 value in UTF16 format. If a validity check is required, use
  {@link android.icu.lang.UCharacter#isLegal(int)} on char32 before calling.
  
  @param char32 The input character.
  @return string value of char32 in UTF16 format
  @exception IllegalArgumentException Thrown if char32 is a invalid codepoint.