How to generate random numbers in Java
A random number is a value chosen without any predictable pattern. Random numbers within a specific range of type integer, float, double, long, and boolean can be generated in Java. In this Answer, we will learn four methods to generate random numbers in Java.
- Using the
java.util.randomclass - Using the
Math.random()method - Using the
ThreadLocalRandomclass - Using the
SecureRandomclass
Method 1: Using the java.util.random class
To use the Random Class to generate random numbers, follow the steps below:
- Import the class
java.util.Random - Make the instance of the class
Random, i.e.,Random rand = new Random() - Invoke one of the following methods of
randobject:nextInt(upperbound)generates random numbers in the range 0 toupperbound-1.nextFloat()generates a float between 0.0 and 1.0.nextDouble()generates a double between 0.0 and 1.0.
import java.util.Random;class GenerateRandom {public static void main( String args[] ) {// Instance of random classRandom rand = new Random();// Setting the upper bound to generate the// random numbers in specific rangeint upperbound = 25;// Generating random numbers from 0 - 24// using nextInt()int int_random = rand.nextInt(upperbound);// Generating random numbers using nextDouble// in 0.0 and 1.0 rangedouble double_random = rand.nextDouble();// Generating random numbers using nextFloat// in 0.0 and 1.0 rangefloat float_random = rand.nextFloat();// Printing the generated random numbersSystem.out.println("Random integer value from 0 to" + (upperbound-1) + " : " + int_random);System.out.println("Random float value between 0.0 and 1.0 : " + float_random);System.out.println("Random double value between 0.0 and 1.0 : " + double_random);}}
This class also allows us to generate long and boolean type random numbers using the nextLong() and nextBoolean() methods, respectively. You can see examples of these methods in this Answer.
Method 2: Using the Math.random() method
The Math.random() function in Java generates a double-type random number between 0 (including) and 1 (excluding).
class GenerateRandom {public static void main( String args[] ) {// Generate random numberSystem.out.println("Random number: " + Math.random());}}
For generating random numbers within a range using the Math.random(), follow the steps below:
- Declare the minimum value of the range
- Declare the maximum value of the range
- Use the formula
Math.floor(Math.random() *(max - min + 1) + min)to generate values with theminand themaxvalue inclusive.
Note: This method can only be used if you need an integer or float random value.
class GenerateRandom {public static void main( String args[] ) {int min = 50; // Minimum value of rangeint max = 100; // Maximum value of range// Print the min and maxSystem.out.println("Random value in int from "+ min + " to " + max + ":");// Generate random int value from min to maxint random_int = (int)Math.floor(Math.random() * (max - min + 1) + min);// Printing the generated random numbersSystem.out.println(random_int);}}
Method 3: Using the ThreadLocalRandom class
To generate random numbers using the class ThreadLocalRandom, follow the steps below:
- Import the class
java.util.concurrent.ThreadLocalRandom - Invoke one of the following methods:
- To generate random number of type int
ThreadLocalRandom.current().nextInt() - To generate random number of type double
ThreadLocalRandom.current().nextDouble() - To generate random number of type boolean
ThreadLocalRandom.current().nextBoolean()
- To generate random number of type int
import java.util.concurrent.ThreadLocalRandom;class GenerateRandom {public static void main( String args[] ) {// Generate random integersint int_random = ThreadLocalRandom.current().nextInt();// Print random integersSystem.out.println("Random Integers: " + int_random);// Generate random doublesdouble double_rand = ThreadLocalRandom.current().nextDouble();// Print random doublesSystem.out.println("Random Doubles: " + double_rand);// Generate random booleansboolean boolean_rand = ThreadLocalRandom.current().nextBoolean();// Print random booleansSystem.out.println("Random Booleans: " + boolean_rand);}}
Method 4: Using the SecureRandom class
Random class has a higher chance of repeating numbers during random number generation. Whereas, SecureRandom class allows us to generate cryptographically strong random numbers using the following steps:
- Import the
SecureRandomusingjava.security.SecureRandom. - Make the instance of
SecureRandomclass usingnew SecureRandom(). - Use following methods to generate the random numbers:
nextInt(upperbound)generates random numbers in the range 0 toupperbound-1.nextFloat()generates a float between 0.0 and 1.0.nextDouble()generates a double between 0.0 and 1.0.
import java.security.SecureRandom;class GenerateRandom {public static void main( String args[] ) {// Instance of SecureRandom classSecureRandom rand = new SecureRandom();// Setting the upper bound to generate// the random numbers between the specific rangeint upperbound = 1000;// Generating random numbers from 0 - 999// using nextInt()int int_random1 = rand.nextInt(upperbound);int int_random2 = rand.nextInt(upperbound);// Generating random numbers using nextDouble// in 0.0 and 1.0 rangedouble double_random = rand.nextDouble();// Generating random numbers using nextFloat// in 0.0 and 1.0 rangefloat float_random = rand.nextFloat();// Printing the generated random numbersSystem.out.println("Random integer value from 0 to " + (upperbound - 1) + " : " + int_random1);System.out.println("Random integer value from 0 to " + (upperbound - 1) + " : " + int_random2);System.out.println("Random float value between 0.0 and 1.0 : " + float_random);System.out.println("Random double value between 0.0 and 1.0 : " + double_random);}}
If you're interested in exploring an alternative method for generating random numbers in Java, check out this Answer, where we discuss Random.ints().
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