Java Random

Java Random class is used to generate a series of random numbers.

Java Random Class

• Random class is part of java.util package.
• An instance of java Random class is used to generate random numbers.
• This class provides several methods to generate random numbers of type integer, double, long, float etc.
• Random number generation algorithm works on the seed value. If not provided, seed value is created from system nano time.
• If two Random instances have same seed value, then they will generate same sequence of random numbers.
• Java Random class is thread-safe, however in multithreaded environment it’s advised to use java.util.concurrent.ThreadLocalRandom class.
• Random class instances are not suitable for security sensitive applications, better to use java.security.SecureRandom in those cases.

Java Random Constructors

Java Random class has two constructors which are given below:

1. Random(): creates new random generator
2. Random(long seed): creates new random generator using specified seed

Java Random Class Methods

Let’s have a look at some of the methods of java Random class.

1. nextBoolean(): This method returns next pseudorandom which is a boolean value from random number generator sequence.
2. nextDouble(): This method returns next pseudorandom which is double value between 0.0 and 1.0.
3. nextFloat(): This method returns next pseudorandom which is float value between 0.0 and 1.0.
4. nextInt(): This method returns next int value from random number generator sequence.
5. nextInt(int n): This method return a pseudorandom which is int value between 0 and specified value from random number generator sequence.

Java Random Example

Let’s have a look at the below java Random example program.

package com.journaldev.examples;

import java.util.Random;

/**
 * Java Random Number Example Program
 * 
 */
public class RandomNumberExample {

	public static void main(String[] args) {
		
		//initialize random number generator
		Random random = new Random();
		
		//generates boolean value
		System.out.println(random.nextBoolean());
		
		//generates double value
		System.out.println(random.nextDouble());
		
		//generates float value
		System.out.println(random.nextFloat());
		
		//generates int value
		System.out.println(random.nextInt());
		
		//generates int value within specific limit
		System.out.println(random.nextInt(20));

	}

}

Output of the above program is:

false
0.30986869120562854
0.6210066
-1348425743
18

Check this post for more about Java Radom Number Generation.

Generate Random Number using Seed

There are two ways we can generate random number using seed.

Random random = new Random(long seed);
                         
Random random1 = new Random();
random1.setSeed(seed);

The seed is the initial value of the internal state of the pseudorandom number generator which is maintained by method next(int).

package com.journaldev.examples;

import java.util.Random;

/**
 * Java Random Number Using Seed Example Program
 * 
 * @author pankaj
 *
 */
public class RadomSeedExample {

	public static void main(String[] args) {
		
		//using constructor
		Random random = new Random(100);
		System.out.println("Using Constructor");
		System.out.println(random.nextInt());
		
		//using method
		Random random2 = new Random();
		random2.setSeed(200);
		System.out.println("Using Method");
		System.out.println(random2.nextInt());
	}
}

Output of the above program is:

Using Constructor
-1193959466
Using Method
-1133938638

What if we pass same seed to two different random number generators? Let’s have a look at the below program and see what happen if we pass same seed to two different random number generators.

package com.journaldev.examples;

import java.util.Random;

/**
 * Java Random Number Using Same Seed Example Program
 * 
 */
public class RandomNumberSameSeedExample {

	public static void main(String[] args) {
		
		//initialize two random number generators using same seed
		Random random1 = new Random(100);
		Random random2 = new Random(100);
		
		System.out.println(random1.nextInt());
		System.out.println(random2.nextInt());

	}

}

Output of the above program is:

-1193959466
-1193959466

We can see that it will generate same random number if we pass same seed to two different random number generators.

Java 8 Random Class Methods

As you can see from above image, there are many new methods added in Java 8 to Random class. These methods can produce a stream of random numbers. Below is a simple program to generate a stream of 5 integers between 1 and 100.

package com.journaldev.random;

import java.util.Random;
import java.util.stream.IntStream;

public class JavaRandomExample {

	public static void main(String[] args) {

		Random random = new Random();

		// generate stream of 5 ints between 1 to 100
		IntStream ints = random.ints(5, 1, 100);

		ints.forEach(System.out::println);
	}

}

That’s all for a quick roundup on Java Random Class. Reference: API Doc