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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><html> <head> <title>Example Three: <code>CelsiusConverter</code> (The Java™ Tutorials > Creating a GUI with JFC/Swing > Learning Swing by Example)</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; 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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> Learning Swing by Example </div> <div id=LeftBar class=LeftBar_shown> <div id=Contents> <div class="linkLESSON"><a href="index.html">Learning Swing by Example</a></div><div class="linkAHEAD"><a href="example1.html">Example One: Your First Swing Program</a></div><div class="linkAHEAD"><a href="example2.html">Example Two: <code>SwingApplication</code></a></div><div class="nolinkAHEAD">Example Three: <code>CelsiusConverter</code></div><div class="linkAHEAD"><a href="example4.html">Example Four: An Improved <code>CelsiusConverter</code></a></div><div class="linkAHEAD"><a href="example5.html">Example Five: <code>LunarPhases</code></a></div><div class="linkAHEAD"><a href="example6.html">Example Six: <code>VoteDialog</code></a></div><div class="linkAHEAD"><a href="summary.html">Summary</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>Learning Swing by Example</a> </span> <div class=NavBit> <a target=_top href=example2.html>« Previous</a> • <a target=_top href=../TOC.html>Trail</a> • <a target=_top href=example4.html>Next »</a> </div> <div id=PageTitle>Example Three: <code>CelsiusConverter</code></div> <blockquote><!--User Interfaces that Swing: A Quick Start Guide--><!--Example Three: CelsiusConverter-->Our next example, <a class="SourceLink" target="_blank" href="examples/CelsiusConverter.java"><code>CelsiusConverter</code></a>is actually useful: It is a simple conversion tool. The user enters a temperature in degrees Celsius and clicks the <code>Convert...</code> button, and a label displays the equivalent in degrees Fahrenheit. <p><center><IMG SRC="../../figures/uiswing/learn/7CelsiusConverter.gif" WIDTH="303" HEIGHT="85" ALIGN="BOTTOM" ALT="The CelsiusConverter GUI"></center></p>Let's examine the code to see how <code>CelsiusConverter</code> parses the number entered in the <code>JTextField</code>. First, here's the code that sets up the <code>JTextField</code>: <blockquote><pre>JTextField tempCelsius = null;...tempCelsius = new JTextField(5);</pre></blockquote>The integer argument passed in the <code>JTextField</code> constructor--<code>5</code> in the example--indicates the number of columns in the field. This number is used along with metrics provided by the current font to calculate the field's preferred width, which is used by layout managers. This number does not limit how many character the user can enter.<P>We want to perform the conversion when the user clicks the button or presses Enter in the text field. To do so, we add an action event listener to the <code>convertTemp</code> button and <code>tempCelsius</code> text field. <blockquote><pre>convertTemp.addActionListener(this);tempCelsius.addActionListener(this);...public void actionPerformed(ActionEvent event) { //Parse degrees Celsius as a double and convert to Fahrenheit. int tempFahr = (int)((Double.parseDouble(tempCelsius.getText())) * 1.8 + 32); fahrenheitLabel.setText(tempFahr + " Fahrenheit");}</pre></blockquote>The event-handling code goes into the <code>actionPerformed</code> method. It calls the <code>getText</code> method on the text field, <code>tempCelsius</code>, to retrieve the data within it. Next it uses the <code>parseDouble</code> method to parse the text as a double-precision floating-point number before converting the temperature and casting the result to an integer. Finally, it calls the <code>setText</code> method on the <code>fahrenheitLabel</code> to make the label display the converted temperature.<p> </blockquote> <div class=NavBit> <a target=_top href=example2.html>« Previous</a> • <a target=_top href=../TOC.html>Trail</a> • <a target=_top href=example4.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. All rights reserved. <span id=Download></span></div> </div> <div class=PrintHeaders> <b>Previous page:</b> Example Two: <code>SwingApplication</code> <br><b>Next page:</b> Example Four: An Improved <code>CelsiusConverter</code> </div> </body></html> ⌨️ 快捷键说明
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