Java Random Number Method

Random Number methods in Java return random numbers for use in the program. There are two ways to generate a random number in the Java programming language. In order to generate random numbers using Java, you should learn the basic properties of each method through studying examples and a generator program demonstration in Java.

Types of Java Random Number Methods

One way to generate a random number in the Java programming language is by using Math.random. This is an instance of the Math class, and is most commonly used when a single random number is needed in a program. A second way to create a random number in Java is to create a java.util.Random object. This is commonly used when a series of random numbers are needed.

Using Math.random()

Math.random() returns a (pseudo) random double within the range of 0.0 up to 1.0. For example:
//generate a random number:
double randomNumber = Math.random();
//view value of variable randomNumber:
System.out.println(randomNumber);
Example output: 0.46041540179337437

More on Math.random()

Math.random() can be cast to change its type. Additionally, arithmetic operations can be used to convert the returned number to a different range. For example:
//Returns a pseudo-random integer between 0 and 9
int randomNumber = (int)(Math.random()*10);

Using java.util.Random

The Java class java.util.Random generates a (pseudo) random number based on a 48-bit seed.
// import the java.util.Random class:
import java.util.Random;
//instantiate a Random object:
Random randomizer = new Random();
//generate a random integer:
int randomNumber = randomizer.nextInt();
//view value of variable randomNumber:
System.out.println(randomNumber);
Example output: -783604159

More on Using java.util.Random

To specify a number range, use nextInt(int n) to specify the range of 0 (inclusive) to n (exclusive). For example:
//generate a random integer between 0 and 9
Random randomizer = new Random();
int randomNumber = randomizer.nextInt(10);
//generate a random integer between 10 and 19
Random randomizer = new Random();
int randomNumber = randomizer.nextInt(10)+10;

Java Random Number Generator Program

The following is a working Java code that demonstrates simple examples of generating random numbers.
//import Java Random class
import java.util.Random;
//Java main class - full program to demonstrate random number generation
public class RandomNumGeneratorMain {
public static void main(String[] args) {
//use Math.random() to generate random number integer between 0 and 9
int randomNumber1 = (int)(Math.random()*10);
System.out.println("Random #1: " + randomNumber1);
//use java.util.Random to generate random integer between 0 and 9
Random randomizer = new Random();
int randomNumber2 = randomizer.nextInt(10);
System.out.println("Random #2: " + randomNumber2);
//use same java.util.Random object to generate random integer between 0 and 99
int randomNumber3 = randomizer.nextInt(100);
System.out.println("Random #3: " + randomNumber3);
}
}

References

• Sun Java Math Class Documentation
• Sun Java Random Class Documentation