Java Generating Random Numbers - Web Development and Design | Tutorial for Java, PHP, HTML, Javascript Java Generating Random Numbers - Web Development and Design | Tutorial for Java, PHP, HTML, Javascript

Breaking

Post Top Ad

Post Top Ad

Wednesday, January 2, 2019

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:>

No comments:

Post a Comment

Post Top Ad