Threads: Doing Two or More Tasks at Once - Java Tutorial 5.0 英文版

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Trail: Essential Java Classes

Lesson: Threads: Doing Two or More Tasks at Once

This chapter has been updated to reflect features and conventions of the latest release, JDK 5.0. If you notice any errors or omissions (or something you really like), please tell us.

A snapshot of three copies of an applet that animates different sorting algorithms is shown in the following figure. No, this chapter is not about sorting algorithms. But these applets do provide a visual aid to understanding a powerful capability of the Java platform — threads.
                  Bidirectional
 Bubble sort       Bubble sort      Quick sort

          
Note: If you don't see the applet running above, you need to install Java Plug-in, which happens automatically when you install the J2SE JRE or JDK. This applet requires JDK 5.0 or later. You can find more information in the Java Plug-in home page.
Start each of the applets, one by one, by clicking on them with the mouse. You can see each one working its way through the data, sorting it, with shorter lines on the top and longer lines on the bottom. While the applets are sorting, also notice that you can scroll the page or bring up one of your browser's panels; all this is due to threads.
A thread — sometimes called an execution context or a lightweight process — is a single sequential flow of control within a program. You use threads to isolate tasks. When you run one of these sorting applets, it creates a thread that performs the sort operation. Each thread is a sequential flow of control within the same program (the browser). Each sort operation runs independently from the others but at the same time.
What Is a Thread?

Using the Timer and TimerTask Classes

Subclassing Thread and Overriding run

Implementing the Runnable Interface

The Life Cycle of a Thread

Thread Scheduling

Synchronizing Threads

Thread Pools

Summary

Questions and Exercises: Threads

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