各位看看我这个为什么不能保证共享变量线程安全

Question

import java.util.concurrent.atomic.AtomicInteger;

class Test extends Thread {
    private static volatile AtomicInteger initNumber = new AtomicInteger(0);
    private int maxNumber = 8000;

    @Override
    public void run() {
        if (initNumber.get() < maxNumber) {
            initNumber.incrementAndGet();
        } else if (initNumber.get() >= maxNumber) {
            initNumber.set(1);
        }
        System.out.println(initNumber.get());
    }

    public static void main(String[] args) {
        for (int i = 0; i < 10000; i++) {
            Thread thread = new Thread(new Test());
            thread.start();
        }
    }
}

Answer 1

线程类要实现Runable接口，共享变量才能确保线程安全。

 

import java.util.concurrent.atomic.AtomicInteger;

class Test implements Runnable {
    private static volatile AtomicInteger initNumber = new AtomicInteger(0);
    private int maxNumber = 8000;

    @Override
    public void run() {
        if (initNumber.get() < maxNumber) {
            initNumber.incrementAndGet();
        } else if (initNumber.get() >= maxNumber) {
            initNumber.set(1);
        }
        System.out.println(initNumber.get());
    }

    public static void main(String[] args) {
        Test test = new Test();
        for (int i = 0; i < 10000; i++) {
            Thread thread = new Thread(test);
            thread.start();
        }
    }
}