private Format getDefaultFormat() {
        // for numeric cells try user supplied default
        if (defaultNumFormat != null) {
            return defaultNumFormat;
            // otherwise use general format
        }
        defaultNumFormat = new ExcelGeneralNumberFormat(locale, useScientificFormat);
        return defaultNumFormat;
    }
Creates a formatter using the given locale.
fastexcel-core/src/main/java/cn/idev/excel/metadata/format/DataFormatter.java