不同实例的多线程仍然产生相同的结果，如何克服这个问题？

Question

  public class MultiThreadingRandom {            public static void main(String[] args) throws InterruptedException {                MultiThreadingRandom multiThreadingRandom = new MultiThreadingRandom();                ExecutorService executorService = Executors.newFixedThreadPool(2);                geneRan r1= new geneRan();                geneRan r2= new geneRan();                executorService.submit(r1);                executorService.submit(r2);                executorService.shutdown();            }        }            class geneRan  implements Runnable{              int rand_int1=0;            @Override            public   void run() {                // TODO Implement this method                Random rand = new Random();                  rand_int1 = rand.nextInt(1000);                 System.out.println(rand_int1);               // System.out.println(ai.getAndIncrement());            }    }该程序有时会给出 2 个不同的输出，但有时会给出相同的输出。实际上，我对这两个线程使用了 2 个不同的对象，所以为什么它在某些情况下给出相同的结果。无论如何，我只传递 2 个不同的对象及其线程安全代码。那么我如何才能确保在任何情况下生成 2 个不同的随机数。

Answer 1

正如已经评论过的，这与多线程无关。由于数字是随机的，因此它们也有可能相同。

如果你想要 2 个不相同的随机数，你可以这样做：

//Create List of integers

List<Integer> numberPool = new ArrayList<>();

//Initialize list with numbers from 1 to 1000

for(int num = 1; num <= 1000 ; num++) {

    numberPool.add(num);

}

//Randomly shuffle list

Collections.shuffle(numberPool);

//Get first number

System.out.println(numberPool.get(0));

//Get second number

System.out.println(numberPool.get(1));

如果你想以多线程方式访问 numberPool，你可以这样做：

public class NumGeneratorThreadSafe{

    List<Integer> numberPool = new ArrayList<>();

    private int counter = 0;

    public NumGeneratorThreadSafe() {

        for(int i = 1; i <= 1000 ; i++) {

            this.numberPool.add(i);

        }

        Collections.shuffle(this.numberPool);

    }

    public synchronized Integer getRandomNumber() {

        return this.numberPool.get(this.counter++);

    }

    public synchronized void resetCounter() {

        this.counter = 0;

    }

}

希望这可以帮助。

编辑： 为了在线程中使用该类：

public class MultiThreadingRandom {

      public static void main(String[] args) throws InterruptedException {

         ExecutorService executorService = Executors.newFixedThreadPool(2);

         NumGeneratorThreadSafe numGenerator = new NumGeneratorThreadSafe();

         GeneRan r1 = new GeneRan(numGenerator);

         GeneRan r2 = new GeneRan(numGenerator);

         executorService.submit(r1);

         executorService.submit(r2);

         executorService.shutdown();

      }

}

class GeneRan  implements Runnable{

      private NumGeneratorThreadSafe numGenerator;

      public GeneRan(NumGeneratorThreadSafe numGenerator) {

         this.numGenerator = numGenerator;

      }

      @Override

      public void run() {

         int randInt = this.numGenerator.getRandomNumber();

         System.out.println(randInt);

      }

}

Answer 2

这个怎么样

import java.util.Random;

import java.util.concurrent.ExecutionException;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

public class MultiThreadingRandom {

   public static void main(String[] args) throws InterruptedException, ExecutionException {

      ExecutorService executorService = Executors.newFixedThreadPool(2);

      Generun r1 = new Generun();

      executorService.submit(r1);

      Thread.sleep(100);

      executorService.submit(r1);

      executorService.shutdown();

   }

}

class Generun implements Runnable {

   int nextInt = -1;

   int bound = 1000;

   @Override

   public void run() {

      int temp = nextInt;

      nextInt = new Random().nextInt(bound);

      if (temp == nextInt) {

         do {

            nextInt = new Random().nextInt(bound);

         } while (temp == nextInt);

      }

      System.out.println(nextInt);

   }

}