Java课件_LESSON 8 - Threads.pptVIP

Java Programming Language Wu Di 2008 华中科技大学智能互联网技术湖北省重点实验室 华中科技大学智能互联网技术湖北省重点实验室 * LESSON 8: Threads 吴砥 wudi@ Department of Electronics Information Engineering, Huazhong University of Science Technology, Wuhan, P.R.C. * The eight core packages of Java java.awt java.awt.event java.io java.sql java.util java.lang java.applet * Outline What are threads Thread Scheduling Thread Management Summary * What are threads * Why need threads It would be nice if we could “do one thing at a time” and “do it well,” but that is simply not how the world works. It is common today for desktop personal computers to be compiling a program, printing a file and receiving e-mail messages over a network concurrently. * The support of threads Concurrency is important in our lives. Ironically, though, most programming languages do not enable programmers to specify concurrent activities. The Ada programming language developed by the United States Department of Defense made concurrency primitives widely available to defense contractors building command and control systems. * Threads in Java Java is unique among popular general-purpose programming languages in that it makes concurrency primitives available to the applications programmer. The programmer specifies that applications contain threads of execution, each thread designating a portion of a program that may execute concurrently with other threads. * Notion Threads are a relatively recent invention in the computer science world. Although processes, their larger parent, have been around for decades, threads have only recently been accepted into the mainstream. What’s odd about this is that they are very valuable, and programs written with them are noticeably better, even to the casual user. * Creating Threads There are two ways to create a new thread of execution: to declare a class to be a subclass of Thread This subclass should override the run method of class Thread. An instance of the subclass can then be allocated and starte