How do you have java create a random number within two ranges (e.g. 5-10 and 12-17)

Question

I need to create a random number within two ranges, but I do not know how. Could someone help me?

rand(1,5) to generate 1->5, then a rand(1) to decide if should be in the 5-10 or 12-17 range... — Marc B, Jul 03 '15 at 19:08
possible duplicate of [Generating random integers in a range with Java](http://stackoverflow.com/questions/363681/generating-random-integers-in-a-range-with-java) — Henry Zhu, Jul 03 '15 at 19:16

score 0 · Answer 1 · answered Jul 03 '15 at 19:08

0

random numbers are generated between 0-1. let's make numbers<0.5 5-10 and numbers > 0.5 12-17 by simply multiplying them.

answered Jul 03 '15 at 19:08

Alp

3,027
1
13
28

AnkeyNigam · Answer 2 · 2015-07-03T19:33:47.870

Try this :-

class PickRandomFromRange
{
    private final List<Integer> range = new ArrayList<>();

    final void addRange(int min, int max)
    {
        for(int i = min; i <= max; i++)
        {
            this.range.add(i);
        }
    }

    int getRandom()
    {
        return this.range.get(new Random().nextInt(this.range.size()));
    }

    public static void main(String[] args)
    {
        PickRandomFromRange rir = new PickRandomFromRange();
        rir.addRange(5,10);
        rir.addRange(12,17);
        System.out.println(rir.getRandom());
    }
}

The above code will basically just makes a list of all the numbers which are in the ranges you give it, then picks a random number from that list, which is therefore a random number from any of the ranges.

score 0 · Answer 3 · answered Jul 03 '15 at 20:21

I figured out a way, although, I don't know if it is an efficient way of solving my problem.

            if(userInput == 4){
            charNumber = 48+random.nextInt(76);
            if(charNumber>47 && charNumber<58){
                outputFile.print((char)charNumber);
                counter++;
            }
            if(charNumber>64 && charNumber<91){
                outputFile.print((char)charNumber);
                counter++;
            }
            if(charNumber>90 && charNumber<97){
                outputFile.print((char)charNumber);
                counter++
            }

            if(charNumber>96 && charNumber<123){
                outputFile.print((char)charNumber);
                counter++;
            }
        }

score 0 · Answer 4 · answered Jul 04 '15 at 11:18

The ranges 5-10 and 12-17 give you a total of 6 + 6 = 12 possible selections.

Pick a random number from 5 to 16. If the number is 11 or more then add one to it. Adding one effectively inserts the gap in your split range.

Random myRand = new Random();

// Number in range [5 .. 16].
int num = 5 + myRand.nextInt(17);

// Increase numbers beyond the gap.
if (num >= 11) {
  num += 1;
}

How do you have java create a random number within two ranges (e.g. 5-10 and 12-17)

4 Answers4