Defining and Starting a Thread
An application that creates an instance of Thread must provide the code that will run in that thread. There are two ways to do this:
- Provide a Runnable object. The Runnable interface defines a single method, run , meant to contain the code executed in the thread. The Runnable object is passed to the Thread constructor, as in the HelloRunnable example:
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(); >> public class HelloThread extends Thread < public void run() < System.out.println("Hello from a thread!"); >public static void main(String args[]) < (new HelloThread()).start(); >> Notice that both examples invoke 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 the Runnable object can subclass a class other than Thread . The second idiom is easier to use in simple applications, but is limited by the fact that your task class must be a descendant of Thread . This lesson focuses on the first approach, which separates the Runnable task from the Thread 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 include static 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 and Thread object. We’ll examine some of these methods in the following sections.
Interface Runnable
All Known Subinterfaces: RunnableFuture , RunnableScheduledFuture All Known Implementing Classes: AsyncBoxView.ChildState , ForkJoinWorkerThread , FutureTask , RenderableImageProducer , SwingWorker , Thread , TimerTask Functional Interface: This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. The class must define a method of no arguments called run .
This interface is designed to provide a common protocol for objects that wish to execute code while they are active. For example, Runnable is implemented by class Thread . Being active simply means that a thread has been started and has not yet been stopped.
In addition, Runnable provides the means for a class to be active while not subclassing Thread . A class that implements Runnable can run without subclassing Thread by instantiating a Thread instance and passing itself in as the target. In most cases, the Runnable interface should be used if you are only planning to override the run() method and no other Thread methods. This is important because classes should not be subclassed unless the programmer intends on modifying or enhancing the fundamental behavior of the class.
Method Summary
When an object implementing interface Runnable is used to create a thread, starting the thread causes the object’s run method to be called in that separately executing thread.
Method Details
run
When an object implementing interface Runnable is used to create a thread, starting the thread causes the object’s run method to be called in that separately executing thread. The general contract of the method run is that it may take any action whatsoever.
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Runnable run method java
The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. The class must define a method of no arguments called run . This interface is designed to provide a common protocol for objects that wish to execute code while they are active. For example, Runnable is implemented by class Thread . Being active simply means that a thread has been started and has not yet been stopped. In addition, Runnable provides the means for a class to be active while not subclassing Thread . A class that implements Runnable can run without subclassing Thread by instantiating a Thread instance and passing itself in as the target. In most cases, the Runnable interface should be used if you are only planning to override the run() method and no other Thread methods. This is important because classes should not be subclassed unless the programmer intends on modifying or enhancing the fundamental behavior of the class.
Method Summary
When an object implementing interface Runnable is used to create a thread, starting the thread causes the object’s run method to be called in that separately executing thread.
Method Detail
run
When an object implementing interface Runnable is used to create a thread, starting the thread causes the object’s run method to be called in that separately executing thread. The general contract of the method run is that it may take any action whatsoever.
Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2023, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.