java 输出值导致多线程下输出正确

public class AddInteger {

    private int count = 0;

    void addCount() {
        int addcount = 0;
        System.out.println(Thread.currentThread().getId() + Thread.currentThread().getName());
        while (addcount++ < 100000) {
            count += 1;
//            System.out.println(count);
        }
    }

    int getCount() {
        return this.count;
    }
}


public class MultithThread implements Runnable{
    private  AddInteger addInteger=null;

    public MultithThread(AddInteger addInteger) {
        this.addInteger = addInteger;
    }

    @Override
    public void run() {
        addInteger.addCount();

    }
}

public class TestThread {
    public static void main(String[] args) {
        AddInteger addInteger = new AddInteger();
        MultithThread multithThread1 = new MultithThread(addInteger);
        Thread thread = new Thread(multithThread1);

        Thread thread2 = new Thread(multithThread1);
        thread.start();
        thread2.start();
        try {
            thread.join();
            thread2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(addInteger.getCount());
    }
}

如上图所示
如果addCount方法内的输出行被注释掉,则最终在主方法中输出的count会小于20000,接近10000,但如果将输出行取消注释,则一定是20000,这边想半天还是没想通,日后再想