Java implements string with spaces every 4 digits

Today I have a bank card recognition function. I want to add a space to every four digits of the bank card number when it is displayed. It will be much more convenient to check the card number. Record it here

1. Regular expression implementation:

        String bankCard = authStatus.getBankCard();
        String bankCard = "1234567890";
        String regex = "(.{4})";
        bankCard = bankCard.replaceAll(regex,"$1 ");
        System.out.println(bankCard);

// 打印1234 5678 90

2.java code implementation:

        String bankCard1 = "333434343443434344";
        char[] bankArray = bankCard1.toCharArray();
        String bankString = "";
        for(int i=0;i<bankArray.length;i++){
            if(i%4==0 && i>0){
                bankString +=" ";
            }
            bankString += bankArray[i];
        }
        System.out.println(bankString);
     
// 打印结果3334 3434 3443 4343 44