text: public String toFormulaString() {StringBuilder sb = new StringBuilder(64);if (externalWorkbookNumber >= 0) {sb.append('[');sb.append(externalWorkbookNumber);sb.append(']');}if (sheetName != null) {SheetNameFormatter.appendFormat(sb, sheetName);}sb.append('!');sb.append(FormulaError.REF.getString());return sb.toString();}