Generating random numbers

invisibleman18 · March 25th, 2007, 12:49 AM

Hi,

I am currently taking a Java based computer science paper at University and am a beginner.
My current assignment is writing a share trading program where users can decide how many of each type of share they would like to buy/sell and there are 5 time periods.
The value of each share (there are 3 types) at the start is a random value of either 5,6,7,8 or 9. In each new time period, the value of each type of share should either increase by 1, decrease by 1 or remain unchanged, and the change which occurs is random. So I have to generate a random number of -1, 0 or 1 to add to the values from the previous period.
So finally, my question. I know how to use Math.random to get 0 or 1, but how can I also randomly generate a negative number?

Thanks in advance for any help.

dafl00 · March 25th, 2007, 11:26 PM

use the java.util.Random class, for example

Code:

java.util.Random rand = new java.util.Random();
// nextInt returns either 0, 1, or 2 and subtracting by 1 gives -1, 0, or 1
int addor = rand.nextInt(3) - 1;

http://java.sun.com/javase/6/docs/api/

Hope this helps

invisibleman18 · March 26th, 2007, 12:22 AM

Hi,

Thanks for the reply.
That is not actually something we have been taught or shown, but I have managed to work out what to do using Math.random

I've done:
int priceChange = (int)(Math.random()*3) - 1;
This generates a random integer from 0 to 2, then subtracts 1 from this to get an integer from -1 to 1.
Then just add that to the previous period share price to find the new share price
Thanks anyway for your reply.