In this chapter we will take a look at Java's support for multithreaded applications. The ability to create multithreaded applications is critical in distributed computing systems, since in many cases you'll want multiple clients to be able to make requests to agents in your system, and you'd like the agents to be as responsive as possible. Supporting asynchronous transactions introduces some new issues in developing any distributed application, and we'll take a look at how the thread support in Java helps you manage these issues.
The Java API includes two classes that embody the core thread support in the language. These classes are java.lang.Thread and java.lang.Runnable. They allow you to define threads of control in your application, and to manage threads in terms of runtime resources and running state.
As the name suggests, java.lang.Thread represents a thread of control. It offers methods that allow you to set the priority of the thread, to assign a thread to a thread group (more on these in a later section), and to control the running state of the thread (e.g., whether it is running or suspended).
The java.lang.Runnable interface represents the body of a thread. Classes that implement the Runnable interface provide their own run() methods that determine what their thread actually does while running. In fact, run() is the only method defined by the Runnable interface. If a Thread is constructed with a Runnable object as its body, the run() method on the Runnable will be called when the thread is started.
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