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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> Writing Event Listeners </div> <div id=LeftBar class=LeftBar_shown> <div id=Contents> <div class="linkLESSON"><a href="index.html">Writing Event Listeners</a></div><div class="linkAHEAD"><a href="intro.html">Introduction to Event Listeners</a></div><div class="nolinkAHEAD">General Information about Writing Event Listeners</div><div class="linkAHEAD"><a href="eventsandcomponents.html">Listeners Supported by Swing Components</a></div><div class="linkAHEAD"><a href="handling.html">Implementing Listeners for Commonly Handled Events</a></div><div class="linkBHEAD"><a href="actionlistener.html">How to Write an Action Listener</a></div><div class="linkBHEAD"><a href="caretlistener.html">How to Write a Caret Listener</a></div><div class="linkBHEAD"><a href="changelistener.html">How to Write a Change Listener</a></div><div class="linkBHEAD"><a href="componentlistener.html">How to Write a Component Listener</a></div><div class="linkBHEAD"><a href="containerlistener.html">How to Write a Container Listener</a></div><div class="linkBHEAD"><a href="documentlistener.html">How to Write a Document Listener</a></div><div class="linkBHEAD"><a href="focuslistener.html">How to Write a Focus Listener</a></div><div class="linkBHEAD"><a href="internalframelistener.html">How to Write an Internal Frame Listener</a></div><div class="linkBHEAD"><a href="itemlistener.html">How to Write an Item Listener</a></div><div class="linkBHEAD"><a href="keylistener.html">How to Write a Key Listener</a></div><div class="linkBHEAD"><a href="listdatalistener.html">How to Write a List Data Listener</a></div><div class="linkBHEAD"><a href="listselectionlistener.html">How to Write a List Selection Listener</a></div><div class="linkBHEAD"><a href="mouselistener.html">How to Write a Mouse Listener</a></div><div class="linkBHEAD"><a href="mousemotionlistener.html">How to Write a Mouse-Motion Listener</a></div><div class="linkBHEAD"><a href="mousewheellistener.html">How to Write a Mouse-Wheel Listener</a></div><div class="linkBHEAD"><a href="propertychangelistener.html">How to Write a Property Change Listener</a></div><div class="linkBHEAD"><a href="tablemodellistener.html">How to Write a Table Model Listener</a></div><div class="linkBHEAD"><a href="treeexpansionlistener.html">How to Write a Tree Expansion Listener</a></div><div class="linkBHEAD"><a href="treemodellistener.html">How to Write a Tree Model Listener</a></div><div class="linkBHEAD"><a href="treeselectionlistener.html">How to Write a Tree Selection Listener</a></div><div class="linkBHEAD"><a href="treewillexpandlistener.html">How to Write a Tree-Will-Expand Listener</a></div><div class="linkBHEAD"><a href="undoableeditlistener.html">How to Write an Undoable Edit Listener</a></div><div class="linkBHEAD"><a href="windowlistener.html">How to Write Window Listeners</a></div><div class="linkAHEAD"><a href="api.html">Listener API Table</a></div><div class="linkAHEAD"><a href="problems.html">Solving Common Event-Handling Problems</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>Writing Event Listeners</a> </span> <div class=NavBit> <a target=_top href=intro.html>« Previous</a> • <a target=_top href=../TOC.html>Trail</a> • <a target=_top href=eventsandcomponents.html>Next »</a> </div> <div id=PageTitle>General Information about Writing Event Listeners</div> <blockquote>This section discusses several design considerationsto keep in mind when implementing event handlers inyour application. We then introduce you to event objects —small objects that describe each event.In particular, we talk about <code>EventObject</code>,the superclass for all AWT and Swing events.Next, we introduce the concepts of low-level events andsemantic events, recommending that you prefer semanticevents when possible. The remainder of this sectiondiscusses implementation techniques you might use in some event listeners or see in event listeners created byother people or by GUI builders.<ul><li><a href="#design">Design Considerations</a><li><a href="#eventobjects">Getting Event Information: Event Objects</a><li><a href="#twokinds">Concepts: Low-Level Events and Semantic Events</a><li><a href="#eventAdapters">Event Adapters</a><li><a href="#innerClasses">Inner Classes and Anonymous Inner Classes</a><li><a href="#eventHandlers">The EventHandler Class</a></ul><a name="design"></blockquote><h3>Design Considerations</h3></a><blockquote>The most important rule to keep in mind about event listenersthat they should execute very quickly.Because all drawing and event-listening methods are executed inthe same thread, a slow event-listener methodcan make the program seem unresponsive and slow to repaint itself.If you need to perform some lengthy operation as the result of anevent, do it by starting up another thread (or somehow sending a request to another thread) to perform the operation. For help onusing threads, see<a class="TutorialLink" target="_top" href="../concurrency/index.html">Concurrency in Swing</a>.<p>You have many choices on how to implement an event listener.We can't recommend a specific approach because one solutionwon't suit all situations. However, we can give you somehints and show you some techniques that you might see,even if you don't use the same solution in your program.<p>For example, you might choose to implement separate classesfor different kinds of event listeners. This can be an easy architectureto maintain, but many classes can also mean reduced performance.<p>When designing your program, you might want to implementyour event listeners in a class that is not public, but somewheremore hidden. A private implementation is a more secureimplementation.<p>If you have a very specific kind of simple event listener, you might be able to avoid creating a class at all by using the<code>EventHandler</code> class.</blockquote><a name="eventobjects"></blockquote><h3>Getting Event Information: Event Objects</h3></a>⌨️ 快捷键说明
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