Should You Reuse a `java.util.Random` Instance or Create a New One Each Time?

Question

What are the advantages of reusing a `java.util.Random` instance over creating a new instance each time in Java?

import java.util.Random;

public class RandomExample {
    public static void main(String[] args) {
        Random random = new Random(); // Reusable instance
        int randomInt = random.nextInt(100); // Use the instance
        System.out.println(randomInt);
    }
}

Answer

In Java programming, managing instances of classes effectively can lead to better performance and cleaner code. When it comes to the `java.util.Random` class, a common debate is whether to reuse a single instance or to create a new instance every time you need a random number. This article explores the pros and cons of each approach, emphasizing performance, thread safety, and resource management.

import java.util.Random;

public class RandomReuseExample {
    private static final Random RANDOM = new Random(); // Singleton instance

    public static int getRandomInt(int upperBound) {
        return RANDOM.nextInt(upperBound);
    }

    public static void main(String[] args) {
        System.out.println(getRandomInt(100)); // Reuse the same instance
    }
}

Causes

  • Creating a new instance of `java.util.Random` initializes a new random number generator which can lead to performance overhead.
  • Each instance of `java.util.Random` maintains its own state, leading to unpredictable output if instances are not carefully managed.

Solutions

  • Use a single `java.util.Random` instance throughout your class or application to avoid the overhead of multiple instances and to ensure better randomness.
  • Consider thread-safety: If your application is multi-threaded, either synchronize access to a shared instance or use `ThreadLocalRandom` for thread-safe random number generation.

Common Mistakes

Mistake: Creating multiple instances of `Random` in a tight loop, which can produce similar random sequences.

Solution: Reuse a single instance of `Random` to ensure better randomness.

Mistake: Not considering thread safety when using `Random` in a multi-threaded environment.

Solution: Use `ThreadLocalRandom` or synchronize access to the shared `Random` instance.

Helpers

  • java.util.Random
  • Java random number generation
  • Best practices for java.util.Random
  • Thread safety with Random in Java
  • Reusing Random instance in Java

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