Java - 有不同的启动线程的方法吗？

Question

Ok, guys so my teacher uses this code to start a thread if a thread is not already active. But i have been taught that to run threads no matter if its runnable or extending thread, you start it by the start method and not run. But in this case he starts it with run, why is that?

public void start2(Runnable r) {
    if (thread == null) {
        thread = new Thread(new Runnable() {
            public void run() {
                r.run();
                thread = null;
            }
        });
        thread.start();
    }
}

Answer 1

Your teacher starts thread with thread.start() . He just implemented the runnable interface inside the Thread object initialization which is the absolutely correct approach.

Answer 2

A more modern approach would be to use an Executor to run the thread:

ExecutorService executor = Executors.newSingleThreadExecutor();
executor.submit(() -> {
    String threadName = Thread.currentThread().getName();
    System.out.println("Hello " + threadName);
});

You have a better control of the thread:

• Can retrieve some result (with futures)
• Know if your thread is over ( executor.isTerminated() )
• Request/force a shutdown ( executor.awaitTermination() / executor.shutdownNow() ).

These functionalities are not natively supported by the thread.start() that your teacher shows you (which is, by the way, a good way to launch a thread).

For more about Executors, I advice this excellent tutorial .

Answer 3

The r.run(); part in your code is just a method call to your Runnable r input parameter, which will be an implementation of the Runnable interface.

This does not start a thread

It's just a method call that is executes the input's implementation of Run method.
It will execute just like any other method.

Then, the actual thread will start at thread.start();

Long answer:
What is happening here is, first checking the thread variable.
If its null then initialize a new Thread with an anonymus class thread = new Thread(/*here --> */new Runnable() {.... and implementing the run() method.
Inside the run() there is a call, made to the outer method's input param, called Runnable r with r.run(); then set the thread variable to null.
Just outside of the if statement, the teacher starts the thread with thread.start(); .