Java Cookbook, 3rd Edition

Chapter 22. Threaded Java

Introduction

We live in a world of multiple activities. A person may be talking on the phone while doodling or reading a memo. A multifunction office machine may scan one fax while receiving another and printing a document from somebody’s computer. We expect the GUI programs we use to be able to respond to a menu while updating the screen. But ordinary computer programs can do only one thing at a time. The conventional computer programming model—that of writing one statement after another, punctuated by repetitive loops and binary decision making—is sequential at heart.

Sequential processing is straightforward but not as efficient as it could be. To enhance performance, Java offers threading, the capability to handle multiple flows of control within a single application or process. Java provides thread support and, in fact, requires threads: the Java runtime itself is inherently multithreaded. For example, window system action handling and Java’s garbage collection—that miracle that lets us avoid having to free everything we allocate, as others must do when working in languages at or below C level—run in separate threads.

Just as multitasking allows a single operating system to give the appearance of running more than one program at the same time on a single-processor computer, so multithreading can allow a single program or process to give the appearance of working on more than one thing at the same time. With multithreading, applications can handle more ...