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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><HTML><HEAD> <TITLE>Java(TM) Language Basics, Part 1, Lesson 3: Building Applets</TITLE> <META NAME="AUTHOR" CONTENT="Monica Pawlan"> <META NAME="KEYWORDS" CONTENT="programming, basics, Java 2"> <META NAME="OWNER" CONTENT="Editorial/JDC"> <META NAME="revision" CONTENT="@(#)applet.src 1.25 09/24/99 JDC"> <STYLE TYPE="text/css"> <!-- CODE {font-family: Courier, Monospace; font-size: 12pt} PRE {font-family: Courier, Monospace; font-size: 11pt} --> </STYLE></HEAD><!-- Start Body Insert--><BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" ALINK="#FF0000" VLINK="#660066"><!-- End Body Insert--><!-- Start PageTop Insert --><TABLE BORDER="0" CELLSPACING="0" CELLPADDING="0" WIDTH="100%"> <TR ALIGN="CENTER" VALIGN="TOP"> <TD WIDTH="157" ALIGN="LEFT"> <IMG SRC="/images/pixel.gif" HEIGHT="40" WIDTH="40" ALT=""> <A HREF="http://java.sun.com/index.html"><IMG SRC="/images/javalogo52x88.gif" WIDTH="52" HEIGHT="88" ALT="Java Technology 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WIDTH="130" BORDER="0" ALT="How Java Technology is Used Worldwide"></A></TD></TR><TR><TD> <DIV ALIGN="RIGHT"> <A HREF="/servlet/PrintPageServlet"><IMG SRC="/images/printbutton.gif" WIDTH="155" HEIGHT="25" ALT="Print Button" BORDER="0"></A> </DIV></TD></TR><TR><TD> </TD></TR><!-- End NavBar Insert --><!-- START SUB-NAV --><TR> <TD><!-- INSERT SUB-NAV INFO --> </TD></TR><!-- END SUB-NAV --></TABLE><TABLE BORDER="0" CELLPADDING="0" CELLSPACING="0"><TR><TD><FONT FACE="Verdana, Arial, Helvetica, sans-serif"><!-- Template Version 2.0 --><!-- ================== --><!-- Start Main Content --><!-- ================== --><TABLE BORDER="0" CELLPADDING="0" CELLSPACING="0"><TR><TD VALIGN="TOP"><FONT FACE="Verdana, Arial, Helvetica, sans-serif"> <A NAME="top"></A> <DIV ALIGN="RIGHT"> <FONT SIZE="-1"><A HREF="/developer/onlineTraining/index.html">Training Index</A></FONT> <H2>Java<FONT SIZE="-2"><SUP>TM</SUP></FONT> Programming Language Basics, Part 1<BR> <FONT SIZE="3">Lesson 3: Building Applets</FONT></H2> <FONT SIZE="-1">[<A HREF="prog.html"><<BACK</A>] [<A HREF="index.html#contents">CONTENTS</A>] [<A HREF="front.html">NEXT>></A>]</FONT></DIV><P>Like applications, applets are created from classes. However, applets do not have a <CODE>main</CODE> method as an entry point, but instead, have several methods to control specific aspects of applet execution. <P>This lesson converts an application from Lesson 2 toan applet and describes the structure and elements of anapplet. <UL> <LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif"> <A HREF="#convert">Application to Applet</A></FONT> <LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif"> <A HREF="#run">Run the Applet</A></FONT> <LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif"> <A HREF="#struct">Applet Structure and Elements</A></FONT> <LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif"> <A HREF="#package">Packages</A></FONT> <LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif"> <A HREF="#more">More Information</A></FONT></UL><HR><A NAME="convert"></A><H3>Application to Applet</H3>The following code is the <A HREF="./Code/SimpleApplet.java">applet</A> equivalent to the <CODE>LessonTwoB</CODE> application from Lesson 2. The figure below shows how the running applet looks. The structure and elements of the applet code are discussed after the section on how torun the applet just below. <P><IMG SRC="./Art/applet.gif" WIDTH="212" HEIGHT="193" ALT=""><P></FONT><PRE>import java.applet.Applet;import java.awt.Graphics;import java.awt.Color;public class SimpleApplet extends Applet{ String text = "I'm a simple applet"; public void init() { text = "I'm a simple applet"; setBackground(Color.cyan); } public void start() { System.out.println("starting..."); } public void stop() { System.out.println("stopping..."); } public void destroy() { System.out.println("preparing to unload..."); } public void paint(Graphics g){ System.out.println("Paint"); g.setColor(Color.blue); g.drawRect(0, 0, getSize().width -1, getSize().height -1); g.setColor(Color.red); g.drawString(text, 15, 25); }}</PRE><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The <CODE>SimpleApplet</CODE> class is declared <CODE>public</CODE> so the program that runs the applet (a browseror <CODE>appletviewer</CODE>), which is not local tothe program can access it. <A NAME="run"></A><H3>Run the Applet</H3>To see the applet in action, you need an <CODE>HTML</CODE> file with the Applet tag as follows:<P><CODE><HTML><BR><BODY><BR><APPLET CODE=SimpleApplet.class WIDTH=200 HEIGHT=100><BR></APPLET><BR></BODY><BR></HTML><BR></CODE><P>The easiest way to run the applet is with appletviewer shown belowwhere <CODE>simpleApplet.html</CODE> is a file that contains the above HTML code:<P></FONT><PRE> appletviewer simpleApplet.html</PRE><FONT FACE="Verdana, Arial, Helvetica, sans-serif"><BLOCKQUOTE><HR>⌨️ 快捷键说明
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