# Random Integer Generation

Question:
How do I write a Java program that generates random numbers withinlimits, such as 1 to 100, or 1 to 1000?

The java.util package includes a Random class which will generate asequence of pseudo-random numbers. Pseudo-random number sequencesappear to have a random distribution, but have a definite order.Given the same seed, a pseudo-random number generator will alwaysproduce the same sequence of numbers. Therefore, you shouldinitialize the Random class with as random a seed as possible. Usingthe current time as a seed is often sufficient.

However, when apseudo-random number sequence is exhausted, it wraps around and startsagain from the beginning. Consequently, for long-lived applicationsthat generate many random numbers over time, you will want toperiodically reseed your random generator.

The Random class does not provide a generic means of generating randomintegers within a specific range. Rather, it generates a uniformlydistributed set of values between 0 and some upper bound. For doublesand floats it generates a value between 0 and 1. You can use this togenerate arbitrary ranges of random integers. The following exampleprogram provides a random integer generating class that takes care ofconverting a random double into a random integer within a specificrange. It also takes care of reseeding the random number generatorafter the sequence has been in use for a long time.

`import java.util.*;public final class RandomIntGenerator {  public static final int DEFAULT_MIN_RANGE = 1;  public static final int DEFAULT_MAX_RANGE = 100;  int _minRange, _maxRange, _range;  long _numCalls;  Random _random;  public RandomIntGenerator() {    this(DEFAULT_MIN_RANGE, DEFAULT_MAX_RANGE);  }  public RandomIntGenerator(int minRange, int maxRange) {    _random   = new Random(System.currentTimeMillis());    setRange(minRange, maxRange);    _numCalls = 0;  }  public void setRange(int minRange, int maxRange) {    _minRange = minRange;    _maxRange = maxRange;    _range    = maxRange - minRange + 1;  }  public int nextInt() {    double d;    d = ((double)_range)*_random.nextDouble();        if(++_numCalls == Integer.MAX_VALUE) {      // The pseudo-random number sequence is sufficiently      // exhausted that it is time to switch to a new seed.      _numCalls = 0;      _random.setSeed(System.currentTimeMillis());    }    return (_minRange + (int)d);  }  public static final void main(String[] args) {    RandomIntGenerator randomInt;    randomInt = new RandomIntGenerator();    for(int i = RandomIntGenerator.DEFAULT_MIN_RANGE;        i <= RandomIntGenerator.DEFAULT_MAX_RANGE; ++i)      System.out.println(randomInt.nextInt());  }}`
See also  Using Consumer Trust to Help Build Brands On Major Social Platforms

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.