Java线程: Running a simple java thread program output confusion

Question

class Runner extends Thread{
    public void run(){
        for(int i=0;i<5;i++)
        {
            System.out.println("Counting "+i);
        }
    }
}
public class App {
    public static void main(String args[])
    {
        Runner runner1=new Runner();
        runner1.start();
        Runner runner2=new Runner();
        runner2.start();
    }
}

我刚刚学习了 java 中线程的基础知识。预期输出是:

Counting 0
Counting 0
Counting 1
Counting 1
Counting 2
Counting 2
Counting 3
Counting 3
Counting 4
Counting 4

但是我得到这样的输出似乎无法推理出这一点:

Counting 0
Counting 1
Counting 2
Counting 3
Counting 4
Counting 0
Counting 1
Counting 2
Counting 3
Counting 4

Answer 1

如果没有任何类型的同步，就无法预期多个线程的执行顺序(以及指令的交错)。

在您的示例中，您可以通过在循环的每次迭代中放置长时间暂停(Thread.sleep)来获得预期的输出(技术上仍然无法保证，但实际上是不可避免的)。