Java Concurrency 简明教程

ThreadLocalRandom Class

java.util.concurrent.ThreadLocalRandom 是从 jdk 1.7 引入的一个实用程序类，当多个线程或 ForkJoinTasks 需要生成随机数时非常有用。它能提升性能，争用比 Math.random() 方法少。

A java.util.concurrent.ThreadLocalRandom is a utility class introduced from jdk 1.7 onwards and is useful when multiple threads or ForkJoinTasks are required to generate random numbers. It improves performance and have less contention than Math.random() method.

ThreadLocalRandom Methods

以下是 ThreadLocalRandom 类中重要的可用方法的列表。

Following is the list of important methods available in the ThreadLocalRandom class.

Sr.No.

Method & Description

1

public static ThreadLocalRandom current() Returns the current thread’s ThreadLocalRandom.

2

protected int next(int bits) Generates the next pseudorandom number.

3

public double nextDouble(double n) Returns a pseudorandom, uniformly distributed double value between 0 (inclusive) and the specified value (exclusive).

4

public double nextDouble(double least, double bound) Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).

5

public int nextInt(int least, int bound) Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).

6

public long nextLong(long n) Returns a pseudorandom, uniformly distributed value between 0 (inclusive) and the specified value (exclusive).

7

public long nextLong(long least, long bound) Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).

8

public void setSeed(long seed) Throws UnsupportedOperationException.

Example

以下 TestThread 程序展示了 Lock 接口的其中一些方法。此处我们使用了 lock() 获取锁，使用了 unlock() 释放锁。

The following TestThread program demonstrates some of these methods of the Lock interface. Here we’ve used lock() to acquire the lock and unlock() to release the lock.

import java.util.Random;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.ThreadLocalRandom;

public class TestThread {

   public static void main(final String[] arguments) {
      System.out.println("Random Integer: " + new Random().nextInt());
      System.out.println("Seeded Random Integer: " + new Random(15).nextInt());
      System.out.println(
         "Thread Local Random Integer: " + ThreadLocalRandom.current().nextInt());

      final ThreadLocalRandom random = ThreadLocalRandom.current();
      random.setSeed(15); //exception will come as seeding is not allowed in ThreadLocalRandom.
      System.out.println("Seeded Thread Local Random Integer: " + random.nextInt());
   }
}

这将产生以下结果。

This will produce the following result.

Output

Random Integer: 1566889198
Seeded Random Integer: -1159716814
Thread Local Random Integer: 358693993
Exception in thread "main" java.lang.UnsupportedOperationException
        at java.util.concurrent.ThreadLocalRandom.setSeed(Unknown Source)
        at TestThread.main(TestThread.java:21)

此处我们使用了 ThreadLocalRandom 和 Random 类获取随机数。

Here we’ve used ThreadLocalRandom and Random classes to get random numbers.