代码

public class Main {

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

        int n = 100000000;

        long startTime = System.currentTimeMillis();
        List<Integer> list = Collections.synchronizedList(new ArrayList<>());

        List<Thread> threads = new ArrayList<>();

        int process = Runtime.getRuntime().availableProcessors();

        for (int i = 1; i <= process; i++) {
            Thread thread;
            if (i == process) {
                thread = new Thread(new MyThread(list, n / process * (i - 1) + 1, n));
            } else {
                thread = new Thread(new MyThread(list, n / process * (i - 1) + 1, n / process * i));
            }
            thread.start();
            threads.add(thread);
        }

        for (Thread thread : threads) {
            thread.join();
        }
        long endTime = System.currentTimeMillis();
        System.out.println((endTime - startTime) / 1000 + "s");

        FileWriter fw = null;
        try {
            System.out.println("1亿以内有:" + list.size() + "个素数");
            //创建字符输出流对象，负责向文件内写入
            fw = new FileWriter("F:\\text.txt");
            //将str里面的内容读取到fw所指定的文件中
            fw.write(list.toString());
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fw != null) {
                try {
                    fw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }
}

class MyThread implements Runnable {

    private final List<Integer> list;
    private final int start;
    private final int end;

    public MyThread(List<Integer> list, int start, int end) {
        this.list = list;
        this.start = start;
        this.end = end;
    }

    @Override
    public void run() {
        for (int i = start; i <= end; i++) {
            if (i < 2) {
                continue;
            }
            int sqrt = (int) Math.sqrt(i);
            int d;
            for (d = 2; d <= sqrt; ++d) {
                if (i % d == 0) {
                    break;
                }
            }
            if (d > sqrt) {
                list.add(i);
            }
        }
    }
}

运行结果

19s
1亿以内有:5761455个素数