1page.title=Specifying the Code to Run on a Thread
2
3trainingnavtop=true
4@jd:body
5
6<div id="tb-wrapper">
7<div id="tb">
8
9<!-- table of contents -->
10<h2>This lesson teaches you to</h2>
11<ol>
12  <li><a href="#ExtendClass">Define a Class that Implements Runnable</a></li>
13  <li><a href="#RunMethod">Implement the run() Method</a>
14</ol>
15
16<h2>You should also read</h2>
17<ul>
18  <li><a href="{@docRoot}guide/components/processes-and-threads.html">Processes and Threads</a></li>
19</ul>
20
21
22<h2>Try it out</h2>
23<div class="download-box">
24    <a href="{@docRoot}shareables/training/ThreadSample.zip" class="button">Download the sample</a>
25    <p class="filename">ThreadSample.zip</p>
26</div>
27</div>
28
29</div>
30</div>
31
32<p>
33    This lesson shows you how to implement a {@link java.lang.Runnable} class, which runs the code
34    in its {@link java.lang.Runnable#run Runnable.run()} method on a separate thread. You can also
35    pass a {@link java.lang.Runnable} to another object that can then attach it to a thread and
36    run it. One or more {@link java.lang.Runnable} objects that perform a particular operation are
37    sometimes called a <i>task</i>.
38</p>
39<p>
40    {@link java.lang.Thread} and {@link java.lang.Runnable} are basic classes that, on their own,
41    have only limited power. Instead, they're the basis of powerful Android classes such as
42    {@link android.os.HandlerThread}, {@link android.os.AsyncTask}, and
43    {@link android.app.IntentService}. {@link java.lang.Thread} and {@link java.lang.Runnable} are
44    also the basis of the class {@link java.util.concurrent.ThreadPoolExecutor}. This class
45    automatically manages threads and task queues, and can even run multiple threads in parallel.
46</p>
47<h2 id="ExtendClass">Define a Class that Implements Runnable</h2>
48<p>
49    Implementing a class that implements {@link java.lang.Runnable} is straightforward. For example:
50</p>
51<pre>
52public class PhotoDecodeRunnable implements Runnable {
53    ...
54    &#64;Override
55    public void run() {
56        /*
57         * Code you want to run on the thread goes here
58         */
59        ...
60    }
61    ...
62}
63</pre>
64<h2 id="RunMethod">Implement the run() Method</h2>
65<p>
66    In the class, the {@link java.lang.Runnable#run Runnable.run()} method contains the
67    code that's executed. Usually, anything is allowable in a {@link java.lang.Runnable}. Remember,
68    though, that the {@link java.lang.Runnable} won't be running on the UI thread, so it can't
69    directly modify UI objects such as {@link android.view.View} objects. To communicate with
70    the UI thread, you have to use the techniques described in the lesson
71    <a href="communicate-ui.html">Communicate with the UI Thread</a>.
72</p>
73<p>
74    At the beginning of the {@link java.lang.Runnable#run run()} method, set the thread to use
75    background priority by calling
76    {@link android.os.Process#setThreadPriority Process.setThreadPriority()} with
77    {@link android.os.Process#THREAD_PRIORITY_BACKGROUND}. This approach reduces
78    resource competition between the {@link java.lang.Runnable} object's thread and the UI
79    thread.
80</p>
81<p>
82    You should also store a reference to the {@link java.lang.Runnable} object's
83    {@link java.lang.Thread} in the {@link java.lang.Runnable} itself, by calling
84    {@link java.lang.Thread#currentThread() Thread.currentThread()}.
85</p>
86<p>
87    The following snippet shows how to set up the {@link java.lang.Runnable#run run()} method:
88</p>
89<pre>
90class PhotoDecodeRunnable implements Runnable {
91...
92    /*
93     * Defines the code to run for this task.
94     */
95    &#64;Override
96    public void run() {
97        // Moves the current Thread into the background
98        android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND);
99        ...
100        /*
101         * Stores the current Thread in the PhotoTask instance,
102         * so that the instance
103         * can interrupt the Thread.
104         */
105        mPhotoTask.setImageDecodeThread(Thread.currentThread());
106        ...
107    }
108...
109}
110</pre>
111