Random generated number

Question

How would you set up a program using Java to generate a 5 digit number using the following statement:

int n = (int)Math.floor(Math.random()*100000+1)

It also has to print the number generated. I have tried writing this different ways and keep coming up with errors.

Answer 1

One might do:

public class Test {
    public static void main(String[] args) {
        int n = (int)Math.floor(Math.random()*100000+1);
        System.out.println(n);
    }
}

However, this really isn't the preferred way of generating random integers. Check out the Random class.

Answer 2

Random r = new Random();
for (;;) {
  System.out.println(10000 + r.nextInt(90000));
}

Answer 3

A better idea is to generate the number by successively generating 5 random digits. Making the first digit non-zero ensures that the generated number is always 5-digit. I'm posting pseudocode below, it should be easy to convert it into Java code.

A = List(1,2,3,4,5,6,7,8,9)
B = List(0,1,2,3,4,5,6,7,8,9)

output = 0

output=random.choice(A) //first digit from A, no zeros

for i=0 to 4
   output=output*10
   output=output+random.choice(B) //next digits from B, can have zero

return output

Look up the API docs for Random if you are stuck.

Answer 4

There are two ways of looking at your problem. Either you need to make sure the random number generator only produces numbers with exactly five digits (in the range 10000 - 99999) or you need to print the numbers with leading 0s when a number is produced that's too low.

The first approach is best met using Java's Random class.

Random rand = new Random();
int n = rand.nextInt(90000) + 10000;
System.out.println(n);

If you're restricted in some way that you must use the statement in your question, then the second approach is probably what you're after. You can use Java's DecimalFormat class to format a random number with leading zeros before printing.

n = (int)Math.floor( Math.random() * 100000 + 1 );
NumberFormat formatter = new DecimalFormat("00000");
String number = formatter.format(n);
System.out.println("Number with lading zeros: " + number);

Answer 5

A way to get a random number 00000 - 99999 is to use the following.

Random r= new Random();
// possibly too obtuse for most readers. ;)
System.out.println((""+(100000+r.nextInt(100000))).substring(1));