An application that creates an instance ofThread
must provide the code that will run in that thread. There are two ways to do this:Notice that both examples invoke
- Provide a
Runnable
object. TheRunnable
interface defines a single method,run
, meant to contain the code executed in the thread. TheRunnable
object is passed to theThread
constructor, as in theexample:
HelloRunnable
public class HelloRunnable implements Runnable { public void run() { System.out.println("Hello from a thread!"); } public static void main(String args[]) { (new Thread(new HelloRunnable())).start(); } }- Subclass
Thread
. TheThread
class itself implementsRunnable
, though itsrun
method does nothing. An application can subclassThread
, providing its own implementation ofrun
, as in theexample:
HelloThread
public class HelloThread extends Thread { public void run() { System.out.println("Hello from a thread!"); } public static void main(String args[]) { (new HelloThread()).start(); } }Thread.start
in order to start the new thread.Which of these idioms should you use? The first idiom, which employs a
Runnable
object, is more general, because theRunnable
object can subclass a class other thanThread
. The second idiom is easier to use in simple applications, but is limited by the fact that your task class must be a descendant ofThread
. This lesson focuses on the first approach, which separates theRunnable
task from theThread
object that executes the task. Not only is this approach more flexible, but it is applicable to the high-level thread management APIs covered later.The
Thread
class defines a number of methods useful for thread management. These includestatic
methods, which provide information about, or affect the status of, the thread invoking the method. The other methods are invoked from other threads involved in managing the thread andThread
object. We'll examine some of these methods in the following sections.