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SHAPE ="RECT" HREF ="/reference/author.html" COORDS ="361,0,440,29"><AREA SHAPE ="RECT" HREF ="/reference/basic.html" COORDS ="254,0,360,29"><AREA SHAPE ="RECT" HREF ="/reference/help.html" COORDS ="183,0,251,29"><AREA SHAPE ="RECT" HREF ="/reference/cool.html" COORDS ="100,0,181,29"><AREA SHAPE ="RECT" HREF ="/reference/mybook.html" COORDS ="0,0,100,29"></MAP><MAP NAME ="header_r1.gif.map"><AREA SHAPE ="RECT" HREF ="/reference/personalize.html" COORDS ="339,0,439,29"></MAP><p><font face="Arial,Helvetica" size="-1" color="#006666"><A HREF="/reference/r_library.html"><B>All Categories</A> :</B><b><A HREF="/reference/r_java.html">Java</A></b></font><p><META><H1><FONT SIZE=6 COLOR=#Ff0000>Chapter 3</FONT></H1><H1><FONT SIZE=6 COLOR=#Ff0000>Applets and the Internet</FONT></H1><HR><P><CENTER><B><FONT SIZE=5><A NAME="CONTENTS">CONTENTS</A></FONT></B></CENTER><UL><LI><A HREF="#LocalandRemoteApplets">Local and Remote Applets</A><UL><LI><A HREF="#LocalApplets">Local Applets</A><LI><A HREF="#RemoteApplets">Remote Applets</A></UL><LI><A HREF="#ClientsandServers">Clients and Servers</A><LI><A HREF="#Security">Security</A><LI><A HREF="#ExampleYourPagesontheWeb">Example: Your Pages on the Web</A><LI><A HREF="#Summary">Summary</A><LI><A HREF="#ReviewQuestions">Review Questions</A><LI><A HREF="#ReviewExercises">Review Exercises</A></UL><HR><P>Now that you have some idea how you can add Java applets to yourWeb pages, you need to discover how applets are handled on theInternet. After all, it is an applet's ability to hitch a rideon the Information Superhighway that makes it so unique. In fact,applets are really the first step towards making the Interneta true extension of your computer's local storage system. Whenyou view a Web page containing applets, those applets may be comingto you from just about anywhere on the Web-from the office downthe street or from a software distributor in Hong Kong. In thischapter, you discover just how this interaction works.<H2><A NAME="LocalandRemoteApplets"><FONT SIZE=5 COLOR=#Ff0000>Local and Remote Applets</FONT></A></H2><P>One of Java's major strengths is that you can use the languageto create dynamic content for your Web pages. That is, thanksto Java applets, your Web pages are no longer limited to the tricksyou can perform with HTML. Now your Web pages can do just aboutanything you want them to. All you need to do is write the appropriateapplets.<P>But writing Java applets is only half the story. How your Webpage's users obtain and run the applets is equally as important.It's up to you to not only write the applet (or use someone else'sapplet), but also to provide users access to the applet. Basically,your Web pages can contain two types of applets: local and remote.In this section, you learn the difference between these applettypes, which are named after the location at which they are stored.<H3><A NAME="LocalApplets">Local Applets</A></H3><P>A local applet is one that is stored on your own computer system(Figure 3.1). When your Web page must find a local applet, itdoesn't need to retrieve information from the Internet-in fact,your browser doesn't even need to be connected to the Internetat that time. As you can see in Listing 3.1, a local applet isspecified by a path name and a file name.<P><A HREF="f3-1.gif"><B> Figure 3.1 : </B><I>Local applets are stored on and loaded from your computer system.</I></A><P><HR><BLOCKQUOTE><B>Listing 3.1 LST3_1.TXT: Specifying a Local Applet.<BR></B></BLOCKQUOTE><BLOCKQUOTE><PRE><applet codebase="tictactoe" code="TicTacToe.class" width=120 height=120></applet></PRE></BLOCKQUOTE><HR><P>In Listing 3.1, the <TT>codebase</TT> attribute specifies a pathname on your system for the local applet, whereas the <TT>code</TT>attribute specifies the name of the byte-code file that containsthe applet's code. The path specified in the <TT>codebase</TT>attribute is relative to the folder containing the HTML documentthat references the applet. (See the "Optional Attributesfor Applets" section of <A HREF="ch2.htm" >Chapter 2</A>for more information.)<H3><A NAME="RemoteApplets">Remote Applets</A></H3><P>A remote applet is one that is located on another computer system(Figure 3.2). This computer system may be located in the buildingnext door or it may be on the other side of the world-it makesno difference to your Java-compatible browser. No matter wherethe remote applet is located, it's downloaded onto your computervia the Internet. Your browser must, of course, be connected tothe Internet at the time it needs to display the remote applet.<P><A HREF="f3-2.gif"><B> Figure 3.2 : </B><I>Remote applets are stored on another system and are down-loaded onto your computer via the Internet.</I></A><P><P>To reference a remote applet in your Web page, you must know theapplet's URL (where it's located on the Web) and any attributesand parameters that you need to supply in order to display theapplet correctly. If you didn't write the applet, you'll needto find the document that describes the applet's attributes andparameters. This document is usually written by the applet's author.Listing 3.2 shows how to compose an HTML <TT><applet></TT>tag that accesses a remote applet.<HR><BLOCKQUOTE><B>Listing 3.2 LST3_2.TXT: Specifiying a Remote Applet.<BR></B></BLOCKQUOTE><BLOCKQUOTE><PRE><applet codebase="http://www.myconnect.com/applets/" code="TicTacToe.class" width=120 height=120></applet></PRE></BLOCKQUOTE><HR><P>The only difference between Listing 3.1 and Listing 3.2 is thevalue of the <TT>codebase</TT> attribute. In the first case, <TT>codebase</TT>specifies a local folder, and in the second case, it specifiesthe URL at which the applet is located.<H2><A NAME="ClientsandServers"><FONT SIZE=5 COLOR=#Ff0000>Clients and Servers</FONT></A></H2>⌨️ 快捷键说明
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