1. Overview
Random selection of elements from a Set is a common requirement in various Java applications, especially in games and data processing tasks.
In this article, we’ll explore different methods to pick a random element from a Java Set.
2. Using the java.util.Random Class
The java.util.Random class is a handy tool for generating random numbers. To pick a random element from a Set, we can generate a random index and use it to access the element:
public static <T> T getByRandomClass(Set<T> set) {
if (set == null || set.isEmpty()) {
throw new IllegalArgumentException("The Set cannot be empty.");
}
int randomIndex = new Random().nextInt(set.size());
int i = 0;
for (T element : set) {
if (i == randomIndex) {
return element;
}
i++;
}
throw new IllegalStateException("Something went wrong while picking a random element.");
}
Let’s test our method:
Set<String> animals = new HashSet<>();
animals.add("Lion");
animals.add("Elephant");
animals.add("Giraffe");
String randomAnimal = getByRandomClass(animals);
System.out.println("Randomly picked animal: " + randomAnimal);
The result should be random:
Randomly picked animal: Giraffe
3. Using the ThreadLocalRandom Class
Starting from Java 7, the ThreadLocalRandom class provides a more efficient and thread-safe alternative for generating random numbers. Here’s how we can use it to pick a random index from a Set:
int randomIndex = ThreadLocalRandom.current().nextInt(set.size());
The solution is the same as above except for how the random number is selected.
Using ThreadLocalRandom is preferable over java.util.Random because it reduces contention in multi-threaded scenarios and generally offers better performance.
4. Conclusion
In summary, we’ve learned two ways to pick a random element from a Java Set.
The example code from this article can be found over on GitHub.
