java中字符串“abcdefgh”轉換爲“ab:cd:ef:gh”

/**
     * 字符串abcdef變爲ab:cd:ef
     * 
     * @param BLEDeviceMACAddress
     * @return
     */
    private String toString(String BLEDeviceMACAddress) {
        // 字符串abcdef變爲ab:cd:ef
        String regex = "(.{2})";
        BLEDeviceMACAddress = BLEDeviceMACAddress.replaceAll(regex, "$1:").trim();
        BLEDeviceMACAddress = BLEDeviceMACAddress.substring(0, BLEDeviceMACAddress.length() - 1);
        return BLEDeviceMACAddress;
    }

說明：傳進去字符串“abcdefgh”，出來後是“ab:cd:ef:gh”