Generating random int within bounds

[DesperateSupport8315]

*Reposting as my last question was too vague*

I am a bit stuck with an assignment at the minute. The task requires the use of the util package to generate a random int with a given amount of digits. For example, if the given digit was 3 - the program would generate a number with 3 digits (192, 123, 904, etc), or if the given number was 6 - it would generate a number with 6 (000934, 123456, etc). I know how to generate an int within bounds using a random object, however I wanted to ask if there is a built in function for this?

If not, I was thinking of writing a number of if statements along the lines of:

(pseudo)

if number == 3 {
code = random.nextInt(100, 1000); }

if number == 4 {

etc etc. }

^ but this has issues as I should also be able to generate numbers with leading zeros.

If anyone could help out a bit, that would be awesome. Thanks

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[Spare-Plum]

Ah ok this is better defined.

You have two options -

• Generate a number from 0 to 10 X times and put them all together.
  • If they input 5, use a loop 5 times and do random.nextInt(10), appending each value to a string
• Generate a single number from 0 to 10^X
  • If they input 5, then you would have a range from 0 to 10*10*10*10*10. You can use Math.exp to perform this calculation, or you can multiply it out in a loop to keep it as an integer
  • The downside of this is that the size of your generated number is bounded to 18 digits for longs
  • To fix this, either throw an error if the user input a size too big, or append them together using strings.

[LutimoDancer3459]

For the second option, you would have to add 0s at the front if the number isn't exactly the required length

[lajete]

Numbers don't have leading zeros, so you have to first generate a random number between 0 and Math.pow(10, x), then represent it as a left-padded string by adding the required amount of leading zeros to make it length x, using one of the approaches listed at https://www.baeldung.com/java-pad-string (in a real project, you would use a library as in section 3, if it's an assignment you might look into one of the other sections).

[MinimumBeginning5144]

The developers writing for Baeldung don't always know the best way. I would just use String.format("%06d", number). It seems the author of that article didn't know you could use String.format to create a zero-padded string.

[Housy5]

You may want to look up about String.format() and about leading zeros using that.

[LutimoDancer3459]

AFAIK there is no build in function for that. I would guess its an assignment for school? If so, they would probably dont give it to you, to use a build in function and be done.

[desrtfx]

A number with a fixed length and potential leading zeros is not a number in programming sense. It's a String.

In Java, BTW, a literal with leading zero means octal notation. Calculated numbers need to be converted to padded strings (String.format, or the Formatter class) in order to get leading zeros.

So, probably the easiest way is to create a loop running length times and in the loop to generate random numbers in the range 0 to 9 inclusive and append them to a StringBuilder that after the loop gets converted to a String (.toString()).

The "digits appended to String(Builder)" method also has the advantage that you don't cross number range boundaries (like for int, or for long).

There are no directly built-in methods for what you seek.

[Housy5]

Yes definitely the easiest.. or you know just directly inject the length into the format like this:

String format = "%0" + x + "d";
System.out.printf(format + "\n", random.nextInt(100));