Java Random Print

Question

I generate a random number between 0-99 using this :

int num2= (int)(Math.random() * ((99) + 1));

When the number is below 10 I want it to print with a 0num2 So if the number is 9 it would be 09.

How can I get it to print this?

Why not use * 100 directly? Why 99 + 1? – Simon Forsberg Sep 24 '12 at 19:44 — Simon Forsberg, Sep 24 '12 at 19:44
http://stackoverflow.com/a/275716/779982 – naugler Sep 24 '12 at 20:43 — naugler, Sep 24 '12 at 20:43

score 5 · Accepted Answer · edited Sep 24 '12 at 19:47

5

You can use the format() method:

System.out.format("%02d%n", num2);

%02d prints the argument as a number with width 2, padded with 0's
%n gives you a newline

edited Sep 24 '12 at 19:47

Matt Ball

answered Sep 24 '12 at 19:45

Keppil

score 3 · Answer 2 · answered Sep 24 '12 at 19:44

3

System.out.println((num2 < 10 ? "0" : "") + num2);

One liner :-)

answered Sep 24 '12 at 19:44

arshajii

score 2 · Answer 3 · answered Sep 24 '12 at 19:43

2

String str;
if (num2 < 10) str = "0" + num2;
else str = "" + num2;

System.out.println("Value is: " + str);

answered Sep 24 '12 at 19:43

Simon Forsberg

Where's an easy button when you need one? – thatidiotguy Sep 24 '12 at 19:44
Haha, to enjoy the pleasure of pushing it and hearing the phrase "That was easy". – thatidiotguy Sep 24 '12 at 19:48

pb2q · Answer 4 · 2012-09-24T19:49:39.067

Have a look at PrintStream.format, which will allow you to print using specified widths and padding characters.

System.out is a PrintStream, so you can use System.out.format in place of println.

Your case is pretty simple, look over the syntax for the format string:

System.out.format("%02d", num2);

Here 2 is the minimum width, and the 0 specifies that the result be padded with zeros, if the width of the result is less than 2.

score 1 · Answer 5 · answered Sep 24 '12 at 19:46

1

You can use the approach of removing an extra digit instead.

System.out.println(("" + (int)(Math.random()*100 + 100)).substring(1));

or to use the String format.

String s = String.format("%02d", (int)(Math.random()*100));

or

System.out.printf("%02d", (int)(Math.random()*100));

I would generally use the last option as it allows you to combine other strings and print them.

answered Sep 24 '12 at 19:46

Peter Lawrey

Do you think that would be better than appending an extra 0 if needed? If so, why? Also, you're getting a number from 100 to 199, not 0 to 99. But I hope you knew that. – Simon Forsberg Sep 24 '12 at 19:47
After removing the first digit 100 to 199 becomes 00 to 99. As to whether its better is a matter of taste. – Peter Lawrey Sep 24 '12 at 19:49
It makes the code both harder to read and, most likely, slower (even though a very tiny bit)... Don't see any point at all in using substring to do the job. – Simon Forsberg Sep 24 '12 at 19:53

5 Answers5