When an object implementing interface <code>Runnable</code> is used to create a thread, starting the thread causes the object's <code>run</code> method to be called in that separately executing thread. <p> The general contract of the method <code>run</code> is that it may take any action whatsoever.
The <code>Runnable</code> 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 <code>run</code>. <p> This interface is designed to provide a common protocol for objects that wish to execute code while they are active. For example, <code>Runnable</code> is implemented by class <code>Thread</code>. Being active simply means that a thread has been started and has not yet been stopped. <p> In addition, <code>Runnable</code> provides the means for a class to be active while not subclassing <code>Thread</code>. A class that implements <code>Runnable</code> can run without subclassing <code>Thread</code> by instantiating a <code>Thread</code> instance and passing itself in as the target. In most cases, the <code>Runnable</code> interface should be used if you are only planning to override the <code>run()</code> method and no other <code>Thread</code> methods. This is important because classes should not be subclassed unless the programmer intends on modifying or enhancing the fundamental behavior of the class.