如何在不使用Runnable实现的情况下运行线程？

Question

I found the following excerpt in a Java Textbook:

"I've seen examples that don't use a separate 
Runnable Implementation, but Instead Just make a 
subclass of Thread and override the Thread's runO 
method. That way,you call the Thread's no-arg 
constructor when you make the new thread; 
Thread t = new Thread(); //no Runnable"

Shouldn't the last line be

Thread t = new <Some class that extends Thread class and over rides its run method>();

Am I correct?

Could somebody provide sample code that illustrates the above excerpt?

Answer 1

You are correct.

If you create an instance of Thread without overriding run() of supplying a Runnable , the thread would execute the default empty run() method.

I wonder if this quote is accurate, as it specifically mentions sub-classing Thread, but the code Thread t = new Thread(); clearly doesn't.

Answer 2

Basically you are talking about runtime polymorphism. Yes you could do that. See following exmaple:

class Flight extends Thread {
    public void run() {
        System.out.println("Hello World.. I took off");
    }
}

public static void main(String[] args) {
    Flight flight = new Flight();
    Thread myflight = new Flight();//See how i used runtime polymorphism.
    flight.start();
    myflight.start();
}

Answer 3

You can override the run method "inline" with an anonymous subclass:

new Thread() {
    public void run() {
        doStuffInPaarralel();
    }
}.start();

Not that there are a lot of advantages to this over supplying a separate Runnable class. You rearely need a thread, that just does one thing and dies, it's kinda wasteful. A better way is to use a ThreadPool , which has a bunch of threads, that are available for executing any task when you need them. That way, you reduce the overhead of starting up and destroying the thread every time.