Java Generating Random Numbers

Java Generating Random Numbers

Problem

You need to generate random numbers in a hurry.

Solution

Use java.lang.Math.random( ) to generate random numbers. There is no claim that
the random values it returns are very good random numbers, however. This code
exercises the random( ) method:

// Random1.java
// java.lang.Math.random( ) is static, don't need to construct Math
System.out.println("A random from java.lang.Math is " + Math.random( ));

Note that this method only generates double values. If you need integers, you need to scale and round:

/** Generate random ints by asking Random( ) for
* a series of random integers from 1 to 10, inclusive.
*
* @author Ian Darwin, http://www.darwinsys.com/
* @version $Id: ch05,v 1.5 2004/05/04 20:11:35 ian Exp $
*/
public class RandomInt {
public static void main(String[] a) {
Random r = new Random( );
for (int i=0; i<1000; i++)
// nextInt(10) goes from 0-9; add 1 for 1-10;
System.out.println(1+Math.round(r.nextInt(10)));
}
}

To see if it was really working well, I used the Unix tools sort and uniq, which, together, give a count of how many times each value was chosen. For 1,000 integers, each of 10 values should be chosen about 100 times:

C:> java RandomInt | sort -n | uniq -c
110 1
106 2
98 3
109 4
108 5
99 6
94 7
91 8
94 9
91 10
C:>