java - 如果我们在 start 方法而不是 run 方法中执行整个 Thread 功能，会发生什么？

Question

如果我们在 start 方法而不是 run 方法中执行整个 Thread 功能，会发生什么？下面的代码运行方式与我在 run 方法中添加代码时的运行方式相同。

   public class RunMethodTest extends AppCompatActivity {


    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Abc abc=new Abc();
        abc.start();
    }
}

class Abc extends Thread
{
    @Override
    public synchronized void start() {
        super.start();
        for(int i=0;i<10;i++) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("Thread" + " " + i);
        }
    }
}

Answer 1

测试它:让您的代码告诉您它正在被哪个线程调用

1. 通过Thread.currentThread()获取当前线程
2. 然后通过getId()和getName()获取当前线程的id和name

public class ThreadTest {
    public static void main(String[] args) {
        Thread currentThread = Thread.currentThread();
        System.out.printf("Main, Which Thread: %s, %d%n", 
                currentThread.getName(), 
                currentThread.getId());

        Abc abc = new Abc();
        abc.start();
    }
}

class Abc extends Thread {
    @Override
    public synchronized void start() {
        super.start();

        Thread currentThread = Thread.currentThread();
        System.out.printf("Start, Which Thread: %s, %d%n", 
                currentThread.getName(), 
                currentThread.getId());

        for (int i = 0; i < 10; i++) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("Thread" + " " + i);
        }
    }

    @Override
    public void run() {
        super.run();

        Thread currentThread = Thread.currentThread();
        System.out.printf("Run, Which Thread: %s, %d%n", 
                currentThread.getName(), 
                currentThread.getId());
    }
}

对我来说，这返回:

Main, Which Thread: main, 1
Start, Which Thread: main, 1
Run, Which Thread: Thread-0, 9
Thread 0
Thread 1
Thread 2
Thread 3
....

这证明您的 Abc 的 start 方法(如预期)在与调用代码相同的线程中调用，而不是在新线程中调用，并且只有 run() 方法中的代码是在新线程中被调用。正如上面所指出的，您几乎不需要或想要扩展 Thread，而是实现 Runnable 或 Callable。