Java add leading zeros to a number

When areaCode is 0, you forget to call format! Other than that, it looks fine. The leading "#" are not necessary, but won't cause any problems for valid inputs.

I just tried it out real quick to check and it worked fine for me.

public static String formatTest(int areaCode, int exchangeCode, int number) {
    DecimalFormat nf3 = new DecimalFormat("#000");
    DecimalFormat nf4 = new DecimalFormat("#0000");
    if( areaCode != 0)
        return nf3.format(areaCode) + "-" + nf3.format(exchangeCode) + "-" + nf4.format(number);
    else
        return nf3.format(exchangeCode) + "-" + nf4.format(number);
}


public static void main(String[] args) {
    System.out.println(formatTest(12, 90, 8));
    System.out.println(formatTest(1, 953, 1932));
}

Output:

012-090-0008
001-953-1932

There's an arguably more elegant solution:

String.format("%03d-%03d-%04d", areaCode, exchangeCode, number)