class Core {
    private int value;

    public int getSum() {
        for (int i = 0; i < 50000000; i++) {
            value++;
        }
        return value;
    }
}

public class DemoRunnable implements Runnable{

    @Override
    public void run() {
        Core core = new Core();
        int sum = core.getSum();
        try {
            Thread.sleep(100);
        } catch (Exception e) {
            e.printStackTrace();
        }
        
        System.out.println(sum);
    }

}

public class Client {
    public static void main(String[] args) {
        
        DemoRunnable core = new DemoRunnable();
        
        Thread one = new Thread(core);
        Thread two = new Thread(core);
        
        one.start();
        two.start();
    }
}

这段代码的输出结果为

50000000
50000000

为什么会有两行输出结果呢？虽然创建了两个线程，但是执行的是同一个Runnable的实例，那么应该只输出一个“50000000”才对吧？