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This article will introduce three methods to generate doublerandom values ​​between 0 and 1 of primitive types. To demonstrate the randomness of the generated values, we will use a loop to generate ten random double values ​​between 0 and 1.

Math.random()Generate a random double value between 0 and 1 in Java using

MathThe class can be used to perform various mathematical operations. We can also use this class to generate random numbers. Math.random()is a static function that returns a random number between 0 and 1. Here, 0 is inclusive of the generated value and 1 is always exclusive.

In the following example, we use the Math.random()Generate doubletype to generate random values. In the output, we can see that the values ​​are all random.

public class RandomDouble {
  public static void main(String[] args) {
    for (int i = 0; i < 10; i++) {
      double randomDbl = Math.random();

      System.out.println(randomDbl);
    }
  }
}

Output:

0.9537872648347154
0.2863804438195172
0.5815339629441948
0.7734677312115609
0.021051510563543485
0.9064133490694901
0.6833468691871607
0.30655711217738246
0.2730784326888416
0.6804778782692341

Random().nextDouble()Generate a random double value between 0 and 1 in Java using

Another way to generate random numbers between 0 and 1 is with the RandomAccessKey nextDouble(), which is java.util.Randoma part of the RandomAccessKey class. When we Randomcall RandomAccessKey with an object of the RandomAccessKey class nextDouble(), it returns a random value between 0 and 1, as we have seen in the previous examples.

This method is said to be Math.random()more effective than .

import java.util.Random;

public class RandomDouble {
  public static void main(String[] args) {
    Random randomObj = new Random();

    for (int i = 0; i < 10; i++) {
      double randomDbl = randomObj.nextDouble();

      System.out.println(randomDbl);
    }
  }
}

Output:

0.240017494934622
0.08331956619499614
0.4359524465181911
0.5291811081068774
0.38193057731688373
0.6969527822622924
0.5436002348156281
0.32176862575520415
0.07327708002828293
0.9005635171231344

ThreadLocalRandom.current().nextDouble()Generate a random double value between 0 and 1 in Java using

Both of the techniques we have seen in this tutorial are not efficient for multi-threaded systems and may result in poor performance. This is because when we use Randomthe class to generate random numbers, all threads share the same instance, which means that when a change is made in one thread, all other threads are also executed.

To solve this problem, Java introduced ThreadPool in JDK 7 update ThreadLocalRandom. It is a class that runs only on the current thread, thus achieving better performance in a multi-threaded environment.

In the following example, we call nextDouble(), which ThreadLocalRandom.current()generates a double random value using , which returns a randomly generated double value between 0 and 1.

import java.util.concurrent.ThreadLocalRandom;

public class RandomDouble {
  public static void main(String[] args) {
    for (int i = 0; i < 10; i++) {
      double randomDbl = ThreadLocalRandom.current().nextDouble();

      System.out.println(randomDbl);
    }
  }
}

Output:

0.9717084711770174
0.8977374014983726
0.2744375247405819
0.2866498720386894
0.6118970047667582
0.7441044456568308
0.21043457873690274
0.08985457420563114
0.86748682220748
0.18952106607144148