Convert 1 to 01

Question

I have an int between 1 - 99. How do I get it to always be a double digit, ie: 01, 04, 21?

Answer 1

You can do this with NumberFormat:

NumberFormat format = new NumberFormat();
format.setMinimumIntegerDigits(2);
System.out.println(format.format(1));

Note - String.format() is a Java 5 method.

If you're using Java 5 or above you can do:

String.format("%02d", 1);

as mentioned in other answers.

Answer 2

You can do this by

String.format("%02d", 1)

Answer 3

I think, I should add the link to the official Java documentation on formatting numeric outputs.

https://docs.oracle.com/javase/tutorial/java/data/numberformat.html

Sample Snipplet: Prints 00 up to 100

class Main {
    public static void main(String[] args) {
      for(int i=0;i<=100;i++){
        System.out.println(String.format("%02d", i)); 
      }
    }
}

Output:

00
01
...
10
...
100

Answer 4

Or you could just use printf instead of String.format

 for (int i = 0; i <= 100; i++) {
         System.out.printf("%02d%n",i);
    }

Answer 5

Yet another way

String text = (num < 10 ? "0" : "") + num;

EDIT: The code is short enough that the JIT can compile it to nothing. ;)

long start = System.nanoTime();
for(int i=0;i<100000;i++) {
    for(int num=1;num<100;num++) {
        String text = (num < 10 ? "0" : "") + num;
    }
}
long time = System.nanoTime() - start;
System.out.println(time/99/100000);

prints

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