Threads and Concurrent Programming

The java.lang.Thread class contains the public methods shown in Figure 14.4 (the figure contains only a partial list). Note that Thread implements the Runnable interface, which consists simply of the run() method. As we will now see, another way to create a thread is to instantiate a Thread object and pass it a Runnable object that will become its body. This approach allows you to turn an existing class into a separate thread.

A Runnable object is any object that implements the Runnable interface—that is, any object that implements the run() method (Fig. 14.5). The following example provides an alternative way to implement the NumberThread program:

Given this definition, we would then pass instances of this class to the individual threads as we create them:

The NumberPrinter class implements Runnable by defining exactly the same run() that was used previously in the NumberThread class. We then pass instances of NumberPrinter when we create the individual threads. Doing things this way gives exactly the same output as earlier. This example serves to illustrate another way of creating a multithreaded program: 

• Implement the Runnable interface for an existing class by implementing the void run() method, which contains the statements to be executed by that thread. 
• Create several Thread instances by first creating instances of the Runnable class and passing each instance as an argument to the Thread() constructor. 
• For each thread instance, start it by invoking the start() method on it.

SELF-STUDY EXERCISE 

EXERCISE 14.1 Use the Runnable interface to convert the following class into a thread. You want the thread to print all the odd numbers up to its bound: