Add leading zeroes to number in Java? [duplicate]

Question

Is there a better way of getting this result? This function fails if num has more digits than digits, and I feel like it should be in the library somewhere (like Integer.toString(x,"%3d") or something)

static String intToString(int num, int digits) {     StringBuffer s = new StringBuffer(digits);     int zeroes = digits - (int) (Math.log(num) / Math.log(10)) - 1;      for (int i = 0; i < zeroes; i++) {         s.append(0);     }     return s.append(num).toString(); } 

Answer 1

String.format (https://docs.oracle.com/javase/1.5.0/docs/api/java/util/Formatter.html#syntax)

In your case it will be:

String formatted = String.format("%03d", num); 

• 0 - to pad with zeros
• 3 - to set width to 3

Answer 2

Since Java 1.5 you can use the String.format method. For example, to do the same thing as your example:

String format = String.format("%0%d", digits); String result = String.format(format, num); return result; 

In this case, you're creating the format string using the width specified in digits, then applying it directly to the number. The format for this example is converted as follows:

%% --> % 0  --> 0 %d --> <value of digits> d  --> d 

So if digits is equal to 5, the format string becomes %05d which specifies an integer with a width of 5 printing leading zeroes. See the java docs for String.format for more information on the conversion specifiers.