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using Math.random to generate an integer from 1 to 10

Posted on 2001-09-16
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Last Modified: 2011-09-20
from Right

How can I generate a random integer from 1 to 10 using the Math.random() method.
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Question by:Right
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by:jpk041897
ID: 6486365


int intNum = (int) 10 * java.lang.Math.random();

Since Random returns a a double between 0.0 and 1.0, multipling by 10 will return a value between 0.0 and 1.0. Then cast it to an int.
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LVL 92

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by:objects
ID: 6486416
You better off using the nextInt() method in the Random class. And if you're using a JDK prior to 1.2 then here's the code:

public int nextInt(int n)
{
     if (n<=0)
          throw new IllegalArgumentException("n must be positive");

     if ((n & -n) == n)  // i.e., n is a power of 2
         return (int)((n * (long)next(31)) >> 31);

     int bits, val;
     do {
         bits = next(31);
         val = bits % n;
     } while(bits - val + (n-1) < 0);
     return val;
 }
 

Using Math.random() doesn't allow you any control over the random number seeding and will also be slower due to unnecessary floating point arithmetic.
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Lab_Rat earned 300 total points
ID: 6490826
this looks a cool method!
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LVL 92

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by:objects
ID: 6492001
Interesting answer to accept.
Remind me not to answer any of your questions again.
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by:Lab_Rat
ID: 6495335
LOL!

Objects, pitty this isn't rated a hard question! :o(

ahem!

Anyhow, I don't deserve the points (and a 'B' rating for such an amazing answer as mine? bah!), so I'f you want to get the points you deserve from the mods, I wont take offence. (I think Right was just asleep...)

:o)
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LVL 92

Expert Comment

by:objects
ID: 6495404
Lab Rat,

It's not worth worrying about.
Thanks for the concern :)
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