Mind you, if the smallest value you're allowed to have is 1, then use:
int number = (int ) (Math.random() * 20) + 1 ;
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Question
Unique random numbers in Java
Hi,
How unique random numbers within a range(eg. 1 to 20) can be generated in Java?
Regards.
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Answers
If you are so much particular about UNIQUE random number, please follow the link which discuss about pseudo random number. http://mindprod.com/jgloss
If by 'unique' you mean the numbers must be different each time, you need to use a array. Maybe this is a homework assignment so I'll leave the details to you. Start with all of the allowed numbers in an array. Choose a number from 0 to 19 and read the number from that position in the array. Replace it by the last item(19) and next time choose a number from 0 to 18 etc.
public class RandomGenerator {
private boolean[] used;
private int generated;
public RandomGenerator( int max )
{
used = new boolean[max];
reset();
}
public void reset() {
for( int i = 0; i < max; i++ )
used[i] = false;
generated = 0;
}
public int getNextRandom() {
if( generated == max )
throw new Exception( "Cannot generated more UNIQUE numbers!" );
int index = (int)(Math.random() * max);
while( used[index] )
index = (int)(Math.random() * max);
used[index] = true;
generated++;
return index;
}
}
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by: InteractiveMindPosted on 2005-11-23 at 01:01:32ID: 15348525
int number = (int ) (Math.random() * (20+1)) ;