Creating random numbers within a range

Question

I am very new to Java and I am stuck on this, I am using the formula:

min + (int)(Math.random()*(max-min+1))

and I have to write statements that assign random integers to the variable x in the following ranges

1 < x <= 8
1 being min and 8 being max

Am I correct that it would be 1 + (int)(Math.random()*(8-1+1))?
-5 < x <= 3
3 being min and -5 being max

and this would be 3 + (int)(Math.radom()*(-5-3+1))?

Any help would be greatly appreciated.

have you tried running your code with what you have written? [Math.random](http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html#random()) gives you a random number between 0 and 1, the rest should be easy — senseiwu, Oct 29 '13 at 16:05
A search of SO reveals this as first hit: http://stackoverflow.com/a/363692/791406 — raffian, Oct 29 '13 at 16:07
Substitute `0`, then `1`, as `Math.random()` and see what you get. — Bernhard Barker, Oct 29 '13 at 16:07
You need to check your math, me thinks... `(Math.random()*(8-1+1))` is no different than `Math.random()*7`. I'm not saying it's wrong, just... excessive. — Shaded, Oct 29 '13 at 16:08
@Dukeling I think you mean substitute 0 and 1 as that's the range for `Math.random()`. — Shaded, Oct 29 '13 at 16:09
@Shaded So what would you simplify `max - min + 1` to? Your comment doesn't make a lot of sense to me. — Duncan Jones, Oct 29 '13 at 16:09
@DuncanJones Ah you're right, if you just plugging in for the initial equation, I thought he was hardcoding those values. My mistake, thanks for the correction! — Shaded, Oct 29 '13 at 16:11

score 3 · Answer 1 · answered Oct 29 '13 at 16:12

You want a formula to take a real number in the range [0..1), and return an integer in the range [1..8].

When random() picks a real number it the range [0..1),
and you multiply it by 8,
you get a value in the range [0.0 .. 8.0).
Then you then convert to (int), you have an integer in the range [0 .. 7],
because conversion to (int) rounds using the 'floor' step function.
Add one.

Shamse Alam · Answer 2 · 2013-10-29T16:29:26.483

use following code. It will generate nos between 0 and max value supplied.

 Random generator = new Random(); //Creates a new random number generator
  for(int i=0; i<100; i++){
      /**
       *Returns a pseudorandom, uniformly distributed int value
       * between 0 (inclusive) and the specified value (exclusive), drawn from
       * this random number generator's sequence
       */
        System.out.println(generator.nextInt(100));
  }

Mengjun · Answer 3 · 2013-10-29T16:45:22.147

Get random value with range ( min, max ] , this is the same with the question.

If JDK 1.7 version is used, then you can use one line code to implement such function:

ThreadLocalRandom.current().nextInt(min, max)+1

If JDK version is under 1.7, we can implement it using the following way.

Random random = new Random();

random.nextInt(max - min) + min +1;

2.Get random value with range [ min, max )

Use, ThreadLocalRandom.current().nextInt(min, max)

or

random.nextInt(max - min) + min ;

score 0 · Answer 4 · answered Oct 29 '13 at 16:52

Math.random() gives you between 0 and 1. Multiply this by your range, the size of the range, not the absolute value. If you want 1-10 that's 9, if you want 0-10 that's 10, if you want 5-7 that's 2, etc.

Then add or subtract to go from 0 to the starting value.

If you want 0-9 then you're done (you should have multiplied by 9 in the previous step)

If you want 1-10 then add 1

If you want -5 to 5 then subtract 5

If you want 5-7 then do (Math.random()*2)+5;

Creating random numbers within a range

4 Answers4