Question

我知道我可以使用callables来获取返回值但是可以在不使用它的情况下解决这个问题吗？

我试图从primeThread获取tempCounter值并将它们全部添加到计数器中。但是我收到了“未找到符号”错误。

我可以从PrimeCounter类中的arrayList调用runnable方法吗？

public class PrimeCounter {

public static void countPrimes() {
    int counter = 0;
    int primeNumbers = 2_534_111;
    final int NUM_OF_THREAD = 4;
    int startRange = 2;
    int range = primeNumbers / NUM_OF_THREAD;
    int endRange = startRange + range;

    ArrayList<Thread> threadList = new ArrayList<Thread>();

    for (int i = 0; i < NUM_OF_THREAD; i++) {
        threadList.add(new Thread(new primeThread(startRange, endRange)));
        startRange += range;
        if (endRange + range < primeNumbers) {
            endRange += range;
        } else {
            endRange = primeNumbers;
        }
    }

    for (Thread t : threadList) {
        t.start();
        try {
            t.join();
        } catch (InterruptedException e) {
            System.out.println("Interrupted");
        }
    }

    for (int i = 0; i < threadList.size(); i++) {
        Thread tempThread = threadList.get(i);
        while (tempThread.isAlive()) {
            counter += tempThread.getCounter(); // symbol not found
        }
    }

    System.out.println("\nNumber of identified primes from 2 to " + primeNumbers + " is :" + counter);
}

// checks if n is a prime number. returns true if so, false otherwise
public static boolean isPrime(long n) {
    //check if n is a multiple of 2
    if (n % 2 == 0) {
        return false;
    }
    //if not, then just check the odds
    for (long i = 3; i * i <= n; i += 2) {
        if (n % i == 0) {
            return false;
        }
    }
    return true;
}

primeThread Runnable

class primeThread implements Runnable {
private int startRange;
private int endRange;
private int threadCounter = 0;

public primeThread(int startRange, int endRange) {
    this.startRange = startRange;
    this.endRange = endRange;
}

@Override
public void run() {
    for (int i = startRange; i < endRange; i++) {
        if (Dumb.isPrime(i)) {
            threadCounter++;
        }
    }
}

public int getCounter() {
    return threadCounter;
}

Answer 1

首先阅读Java naming convention（您的班级名称不符合惯例）

使用这个片段你说每个线程都要启动，然后在下一步开始主线程之前等待这个线程的终止（你真的想要这个吗？）：

for (Thread t : threadList) {
    t.start();
    try {
        t.join();
    } catch (InterruptedException e) {
        System.out.println("Interrupted");
    }
}

最后，您从arrayList获取一个线程，并尝试运行此线程不具备的方法。

for (int i = 0; i < threadList.size(); i++) {
    Thread tempThread = threadList.get(i);
    while (tempThread.isAlive()) {
        counter += tempThread.getCounter(); // symbol not found
    }
}

getCounter是primeThread类的方法，但你有Thread类！

如果您的班级 primeThread扩展了Thread类，则可以解决此问题。

无法为ArrayList <thread>中的Runnable调用getter？

1 个答案: