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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><html> <head> <title>How to Use Swing Timers (The Java™ Tutorials > Creating a GUI with JFC/Swing > Using Other Swing Features)</title><style type="text/css"> .FigureCaption { margin-left: 1in; margin-right: 1in; font-family: sans-serif; font-size: smaller; text-align: justify; } #TopBar_bl { background: url(../../images/java_bar_bl.gif) 0 100% no-repeat; width: 100%; height: 60px; } #TopBar_br { background: url(../../images/java_bar_br.gif) 100% 100% no-repeat; width: 100%; height: 60px; } #TopBar_tl { background: url(../../images/java_bar_tl.gif) 0 0 no-repeat; width: 100%; height: 60px; } #TopBar_tr { background: url(../../images/java_bar_tr.gif) 100% 0 no-repeat; width: 100%; height: 60px; } #TopBar { background: #35556B url(../../images/java_bar.gif); margin: 10px 10px 0 10px; height:60px; min-width:700px; color: white; font-family: sans-serif; font-weight: bold; } @media print { #BreadCrumbs, #Download { display: none; } } #TopBar_right { line-height: 14px; 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var main = document.getElementById("MainFlow"); var toggle = document.getElementById("ToggleLeft"); if (b) { contents.className = "LeftBar_shown"; main.className = "MainFlow_indented"; toggle.innerHTML = "Hide the TOC"; document.cookie = 'tutorial_showLeftBar=yes; path=/'; } else { contents.className = "LeftBar_hidden"; main.className = "MainFlow_wide"; toggle.innerHTML = "Show the TOC"; document.cookie = 'tutorial_showLeftBar=no; path=/'; } } function toggleLeft() { showLeft(document.getElementById("LeftBar").className == "LeftBar_hidden"); document.getElementById("ToggleLeft").blur(); } function load() { showLeft(leftBar()); document.getElementById("ToggleLeft").style.display="inline"; } </script> </head><body onload="load()"> <div id=TopBar> <div id=TopBar_tr> <div id=TopBar_tl> <div id=TopBar_br> <div id=TopBar_bl> <div id=TopBar_right> <a target="_blank" href="http://java.sun.com/javase/6/download.jsp">Download the JDK</a> <br> <a href="../../search.html" target="_blank">Search the Tutorials</a> <br> <a href="javascript:toggleLeft()" id="ToggleLeft">Hide the TOC</a> </div> </div> </div> </div> </div> </div> <div class=PrintHeaders> <b>Trail:</b> Creating a GUI with JFC/Swing <br><b>Lesson:</b> Using Other Swing Features </div> <div id=LeftBar class=LeftBar_shown> <div id=Contents> <div class="linkLESSON"><a href="index.html">Using Other Swing Features</a></div><div class="linkAHEAD"><a href="action.html">How to Use Actions</a></div><div class="nolinkAHEAD">How to Use Swing Timers</div><div class="linkAHEAD"><a href="access.html">How to Support Assistive Technologies</a></div><div class="linkAHEAD"><a href="focus.html">How to Use the Focus Subsystem</a></div><div class="linkAHEAD"><a href="keybinding.html">How to Use Key Bindings</a></div><div class="linkAHEAD"><a href="problems.html">Solving Common Problems Using Other Swing Features</a></div></div> </div> <div id=MainFlow class=MainFlow_indented> <span id=BreadCrumbs> <a href=../../index.html target=_top>Home Page</a> > <a href=../index.html target=_top>Creating a GUI with JFC/Swing</a> > <a href=index.html target=_top>Using Other Swing Features</a> </span> <div class=NavBit> <a target=_top href=action.html>« Previous</a> • <a target=_top href=../TOC.html>Trail</a> • <a target=_top href=access.html>Next »</a> </div> <div id=PageTitle>How to Use Swing Timers</div> <blockquote>A Swing timer(an instance of<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/Timer.html"><code>javax.swing.Timer</code></a>) fires one or more action eventsafter a specified delay.Don't confuse Swing timers with the general-purpose timer facility that was addedto the <code>java.util</code> package in release 1.3.This page describes only Swing timers.<p>In general, we recommend using Swing timersrather than general-purpose timersfor GUI-related tasks because Swing timersall share the same, pre-existing timer threadand the GUI-related task automaticallyexecutes on the event-dispatching thread.However, you might use a general-purpose timer ifyou don't plan on touching the GUI from the timer,or need to perform lengthy processing.<p>You can use Swing timers in two ways:<ul><li> To perform a task once, after a delay.<br> For example, the tool tip manager uses Swing timers to determine when to show a tool tip and when to hide it.<li> To perform a task repeatedly.<br> For example, you might perform animation or update a component that displays progress toward a goal.</ul><p>Swing timers are very easy to use.When you create the timer, you specify anaction listener to be notified when thetimer "goes off". The <code>actionPerformed</code>method in this listener should contain the code forwhatever task you need to be performed.When you create the timer, you also specify thenumber of milliseconds between timer firings.If you want the timer to go off only once, you caninvoke <code>setRepeats(false)</code> on the timer.To start the timer, call its <code>start</code> method.To suspend it, call <code>stop</code>.<p>Note that the Swing timer's task is performed in the event dispatch thread.This means that the task can safelymanipulate components,but it also means thatthe task should execute quickly.If the task might take a while to execute,then consider using a <code>SwingWorker</code>instead of or in addition to the timer.See<a class="TutorialLink" target="_top" href="../concurrency/index.html">Concurrency in Swing</a>for instructions about using the <code>SwingWorker</code> classand information on using Swing components in multi-threaded programs.<p>Let's look at an example of using a timerto periodically update a component.The <a class="SourceLink" target="_blank" href="../components/examples/TumbleItem.java"><code><code>TumbleItem</code></code></a>applet uses a timer to update its display at regular intervals. (Tosee this applet running, go to <a class="TutorialLink" target="_top" href="../components/applet.html">How to Make Applets</a>. This applet begins by creating and starting a timer:<blockquote><pre>timer = new Timer(speed, this);timer.setInitialDelay(pause);timer.start(); </pre></blockquote>The <code>speed</code> and <code>pause</code> variables representapplet parameters; as configured on the other page, these are 100 and1900 respectively, so that the first timer even will occur inapproximately 1.9 seconds, and recur every 0.1 seconds. By specifying<code>this</code> as the second argument to the <code>Timer</code>constructor, <code>TumbleItem</code> specifies that it is the actionlistener for timer events.<p>After starting the timer, <code>TumbleItem</code> begins loading aseries of images in a background thread. Meanwhile, the timer eventsbegin to occur, causing the <code>actionPerformed</code> method to execute:<blockquote><pre>public void actionPerformed(ActionEvent e) { //If still loading, can't animate. if (!worker.isDone()) { return; } loopslot++; if (loopslot >= nimgs) { loopslot = 0; off += offset; if (off < 0) { off = width - maxWidth; } else if (off + maxWidth > width) { off = 0; } } animator.repaint(); if (loopslot == nimgs - 1) { timer.restart(); }}</pre></blockquote>Until the images are loaded, <code>worker.isDone</code> returns<code>false</code>, so timer events are effectively ignored. Thefirst part of the event handling code simply sets values that areemployed in the animation control's <code>paintComponent</code>method: <code>loopslot</code> (the index of the next graphic in theanimation) and <code>off</code> (the horizontal offset of the nextgraphic). <p>Eventually, <code>loopslot</code> will reach the end of the imagearray and start over. When this happens, the code at the end of<code>actionPerformed</code> restarts the timer. Doing this causes ashort delay before the animation sequence begins again. </blockquote> <div class=NavBit> <a target=_top href=action.html>« Previous</a> • <a target=_top href=../TOC.html>Trail</a> • <a target=_top href=access.html>Next »</a> </div> </div> <div id=Footer><div id=TagNotes> Problems with the examples? Try <a target="_blank" href=../../information/run-examples.html>Compiling and Running the Examples: FAQs</a>. <br> Complaints? Compliments? Suggestions? <a target="_blank" href="http://developer.sun.com/contact/tutorial_feedback.jsp">Give us your feedback</a>.<br><br> <a target="_blank" href="../../information/copyright.html">Copyright</a> 1995-2006 Sun Microsystems, Inc. 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