generating Random integers in a range(code)

Question

Possible Duplicate:
Java: generating random number in a range

I am unable to understand what is happenning in class Random and in it's methods. will someone explain it,plz?

or is there any simpler way also to generate random numbers?

Note:I want to understand the code of the function (Random.nextInt),not how to use it.

score 3 · Answer 1 · answered Aug 19 '11 at 10:24

3

If you want random integers between x (inclusive) and y (exclusive), here's what you do:

int yourRandomNumber = new Random().nextInt(y-x) + x;

Example: if you want a random selection of [4,5,6,7], you will do:

int yourRandomNumber = new Random().nextInt(4 /* i.e. 8-4 */) + 4;

answered Aug 19 '11 at 10:24

Sean Patrick Floyd

292,901
67
465
588

I didn't think I'd spell it out in big letters... But you did... ;) I figured the OP could do the add/subtract himself... :) – Erik A. Brandstadmoen Aug 19 '11 at 11:21

Erik A. Brandstadmoen · Answer 2 · 2011-08-23T21:24:40.417

What is difficult to understand? There are methods for generating nearly every type of random number... The one you want is probably this:

 int    nextInt(int n)

Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.

EDIT: You ask how the function actually works. This too is explained in the javadoc of the function. If you're more interested in details, you should probably get the D. Knuth book referenced in the docs (from http://download.oracle.com/javase/1.4.2/docs/api/java/util/Random.html):

An instance of this class is used to generate a stream of pseudorandom numbers. The class uses a 48-bit seed, which is modified using a linear congruential formula. (See Donald Knuth, The Art of Computer Programming, Volume 2, Section 3.2.1.)

If two instances of Random are created with the same seed, and the same sequence of method calls is made for each, they will generate and return identical sequences of numbers. In order to guarantee this property, particular algorithms are specified for the class Random. Java implementations must use all the algorithms shown here for the class Random, for the sake of absolute portability of Java code. However, subclasses of class Random are permitted to use other algorithms, so long as they adhere to the general contracts for all the methods.

The algorithms implemented by class Random use a protected utility method that on each invocation can supply up to 32 pseudorandomly generated bits.

Many applications will find the random method in class Math simpler to use.

thx,but what I need to understand is ,THE CODE of this function. — abhi1289, Aug 23 '11 at 14:01

generating Random integers in a range(code)

2 Answers2