Hello,
I am trying to generate a random number with Java, but random in a specific range. For example, my range is 5-10, meaning that 5 is the smallest possible value the random number can take, and 10 is the biggest. Any other number in between these numbers is possible to be a value, too.
In Java, there is a function random() in the Math class, which returns a double value between 0.0 and 1.0. In the class Random there is a function nextInt(int n), which returns a random value in the range of 0 (inclusive) and n (exclusive). I couldn't find a method, which returns a random value between two numbers.
I have tried the following things, but I still have problems: (minimum and maximum are the smallest and biggest numbers).
Solution 1 :
randomNum = minimum + (int)(Math.random()*maximum);
problem: randomNum takes is assinged values numbers bigger that maximum
Solution 2 :
Random rn = new Random();
int n = maximum - minimum + 1;
int i = rn.nextInt() % n;
randomNum = minimum + i;
problem: randomNum takes is assigned values smaller than minimum.
Could you suggest how to solve my problem, or point me to some references? I have tried also browsing through the archive, and found:
- http://stackoverflow.com/questions/137783/given-a-function-which-produces-a-random-integer-in-the-range-1-to-5-write-a-fu
- http://stackoverflow.com/questions/288739/generate-random-numbers-uniformly-over-entire-range
but I couldn't solve the problem.
Thank you.
One standard pattern for accomplishing this is:
Min + (int)(Math.random() * ((Max - Min) + 1))
The java Math library function Math.random() generates a double value in the range [0,1). Notice this range does not include the 1.
In order to get a specific range of values first you need to multiply by the magnitude of the range of values you want covered.
Math.random() * ( Max - Min )
This returns a value in the range [0,Max-Min).
For example if you want [5,10] you need cover 5 integer values so you use
Math.random() * 5
This would return a value in the range [0,5)
Now you need to shift this range up to the range that you are targeting. You do this by adding the Min value.
Min + (Math.random() * (Max - Min))
You now will get a value in the range [Min,Max). But this is still doesn't include max and you are getting a double value. In order to get the max value included, you need to add 1 to your range parameter (Max - Min) and then truncate the decimal part by casting to an int. This is accomplished via:
Min + (int)(Math.random() * ((Max - Min) + 1))
And there you have it. A random integer value in the range [Min,Max].
special thank
