class Random Generate random numbers

class Random Generate random numbers

Summary: By the time you complete this "class Random Generate random numbers", you will understand of how to generate random numbers in Java.

Introduction to class Random Generate random numbers

Generating different numbers at different times of execution, by the same program, is known as random number generation. Random numbers are useful in software product checking and in developing games (as in Dice). Different techniques and algorithms exist, in the software world, to generate random numbers.

There are two ways to generate random numbers by a Java programmer; one is by using the method java.lang.Math.random() and the other is using the methods of class java.util.Random. Usage of Random class is more flexible. The random() method of Math class generates random numbers of double values within the range of 0 and 1 (both not inclusive). These double values can be of positive or negative. But with Random class, we can produce ints, longs and doubles etc. with seed or without seed. When seed is supplied, we get the same sequence of random numbers every time the program is executed. With a little bit extra code, random numbers within a range can also be produced.

Following is the class signature

public class Random extends Object implements Serializable

Generating Random Numbers

In random number generation, the same code executed at different times, produces different results. Following program illustrates the technique of producing random numbers with and without a seed.

import java.util.Random;
public class RandomNumbers1
{
  public static void main(String args[])
  {					
    Random r1 = new Random();          // without seed
    System.out.println("\t\tGenerating Random numbers without seed value");
    for(int i = 0; i < 5; i++)
    {
       int k = r1.nextInt();
       System.out.print(k + "\t");
    }
                                      // with a seed of 150
    Random r2 = new Random(150);
    System.out.println("\n\t\tGenerating Random numbers with a seed value of 150");
    for(int i = 0; i < 5; i++)
    {
      int k = r2.nextInt();
      System.out.print(k + "\t");
    }
  }
}

Random r1 = new Random();
Random r2 = new Random(150);

The Random class constructor is overloaded – one that takes no parameter and the other that takes an integer value (known as seed ). The first object r1 generates different random numbers at different times of execution. The second object r2, with a seed of 150, generates same set of random numbers at different times of execution. Different seed values generate different sets. The random numbers with a seed value are useful to test and bug-fix the software; when the same values are fed, the output of the application should come the same. Random numbers are not thread-safe. Programmer should take care of with concurrency problems in a multithreaded environment.

Generating Random Numbers within a Range

In some applications, the programmer may be required to generate random numbers within a range as in lottery tickets. The range may be zero to some number or between any two numbers.

import java.util.Random;
public class RangeNumbers2
{
  public static void main(String args[])
  { 
    System.out.println("\t\tNumbers 0 to 200");
    Random r1 = new Random();
    for(int i = 0; i < 5; i++)
    {
       int k = r1.nextInt(200);
       System.out.print(k + "\t");
    }
    System.out.println("\n\t\tNumbers within 10 to 30");
    int startRange = 10, endRange = 30;
    for(int i = 0; i < 5; i++)
    {
      int offsetValue =  endRange - startRange + 1;
      int  baseValue = (int)  (offsetValue * r1.nextDouble());
      int k =  baseValue + startRange;
      System.out.print(k + "\t");
    }
  }
}

Random r1 = new Random();
Random r2 = new Random(150);

The Random class constructor is overloaded – one that takes no parameter and the other that takes an integer value (known as seed ). The first object r1 generates different random numbers at different times of execution. The second object r2 with a seed of 150 generates same set of random numbers at different times of execution. Here, the seed value is 150. Different seed values generate different sets. The random numbers with a seed value is useful to test and bug-fix the software; when the same values are fed, the output of the application should be the same. Random numbers are not thread-safe. Programmer should take care of with concurrency problems in a multithreaded environment.

The nextInt() method returns an integer value and similar methods exist, with Random class, like nextDouble(), nextFloat() and nextLong() etc. that returns a double, float and long values.

The nextInt(200) returns an integer value from 0 to 199. To print between any two values, logic included is self explanatory.

Applications of Random Numbers

The importance of random numbers is increasing day-by-day. Some applications are given below.

1. Applications of games as in dice-ware
2. Applications of testing software for searching or sorting
3. Applications of testing with different input values
4. Applications of encryption to give guarantee for secrecy

The following program uses random() method of Math class to generate random numbers.

public class UsingMathRandom
{
  public static void main(String args[])
  {
    for(int i = 0; i < 5; i++)
    {
      double k = Math.random();
      System.out.println(k);
    }
  }
}

The random() method of Math class produces a double values between 0 to 1.0 (not inclusive both).