Java Random

Filed Under: Java

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 Class, Random Class in Java

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);
	}

}

java random number, java random int stream

That’s all for a quick roundup on Java Random Class.

Reference: API Doc

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