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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"><HTML LANG="en"><HEAD><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css"><META NAME="GENERATOR" CONTENT="Adobe FrameMaker 7.0/HTML Export Filter"><LINK REL="STYLESHEET" HREF="unx_unstr_styles.css" CHARSET="ISO-8859-1" TYPE="text/css"><META name="DC.TITLE" content="Virtual Machine Specification, Java Card Platform, v2.2.2"><TITLE>C H A P T E R 1 - Introduction </TITLE></HEAD><BODY BGCOLOR="#ffffff"><DIV><div class="navbar" align="center"><table dir="LTR" summary="Navigation bar, includes the book title and navigation buttons" width=100% cellpadding="0" cellspacing="0" border="0"><colgroup span="2" width="100%"><col id="1" span="1" width="50%"><col id="2" span="1" width="50%"><tr bgcolor="#cccccc"><td class="navbartitle" align=left rowspan="1" colspan="1" abbr="ChapTitle"> Virtual Machine Specification, Java Card Platform, v2.2.2</td><td valign="top" align="right" rowspan="1" colspan="1" abbr="NavButtons"><a href="index.html"><img src="shared/toc01.gif" title="Table Of Contents" alt="Table Of Contents" width="30" height="26" border="0"></a><a href="JCVMpreface.html"><img src="shared/prev01.gif" title="Previous Chapter" alt="Previous Chapter" width="30" height="26" border="0"></a><a href="JCVM02lang.html"><img src="shared/next01.gif" title="Next Chapter" alt="Next Chapter" width="30" height="26" border="0"></a><a href="ix.html"><img src="shared/index01.gif" title="Book Index" alt="Book Index" width="30" height="26" border="0"></a></td></tr></table><br><br></div></DIV><TABLE DIR="LTR" SUMMARY="Chapter Number" ABBR="ChapNum" WIDTH="100%" BORDER="0"><COLGROUP SPAN="1" WIDTH="100%"><COL ID="1" SPAN="1"><TR><TD ALIGN="right" CLASS="ChapNumber"><SPAN CLASS="ChapNumPrefix"><A NAME="pgfId-51"></A>C H A P T E R </SPAN> <SPAN CLASS="ChapNumNum">1</SPAN><A NAME="49617"></A></TD></TR></TABLE><TABLE DIR="LTR" SUMMARY="Chapter Title" ABBR="ChapTitle" WIDTH="100%" BORDER="0"><COLGROUP SPAN="1" WIDTH="100%"><COL ID="1" SPAN="1" WIDTH="100%"><TR><TD ALIGN="right" CLASS="ChapTitle"><HR SIZE=7 NOSHADE><A NAME="pgfId-1765"></A><A NAME="54169"></A>Introduction</TD></TR></TABLE><H2 CLASS="Head1"><A NAME="pgfId-53"></A><DIV><HR ALIGN=left SIZE=6 WIDTH=15% noshade></DIV>1.1 Motivation</H2><P CLASS="Paragraph"><A NAME="pgfId-55"></A>Java Card technology enables programs written in the Java programming language to be run on smart cards and other small, resource-constrained devices. Developers can build and test programs using standard software development tools and environments, then convert them into a form that can be installed onto a Java Card technology-enabled device. Application software for the Java Card platform is called an applet, or more specifically, a Java Card applet or card applet (to distinguish it from browser applets).</P><P CLASS="Paragraph"><A NAME="pgfId-57"></A>While Java Card technology enables programs written in the Java programming language to run on smart cards, such small devices are far too under-powered to support the full functionality of the Java platform. Therefore, the Java Card platform supports only a carefully chosen, customized subset of the features of the Java platform. This subset provides features that are well-suited for writing programs for small devices and preserves the object-oriented capabilities of the Java programming language.</P><P CLASS="Paragraph"><A NAME="pgfId-59"></A>A simple approach to specifying a Java Card virtual machine would be to describe the subset of the features of the Java virtual machine that must be supported to allow for portability of source code across all Java Card technology enabled devices. Combining that subset specification and the information in <EM CLASS="Emphasis">Java Virtual Machine Specification</EM>, smart card manufacturers could construct their own Java Card technology-based implementations ("Java Card implementations"). While that approach is feasible, it has a serious drawback. The resultant platform would be missing the important feature of binary portability of Java Card applets.</P><P CLASS="Paragraph"><A NAME="pgfId-4038"></A>The standards that define the Java platform allow for binary portability of Java programs across all Java platform implementations. This "write once, run anywhere" quality of Java programs is perhaps the most significant feature of the platform. Part of the motivation for the creation of the Java Card platform was to bring just this kind of binary portability to the smart card industry. In a world with hundreds of millions or perhaps even billions of smart cards with varying processors and configurations, the costs of supporting multiple binary formats for software distribution could be overwhelming.</P><P CLASS="Paragraph"><A NAME="pgfId-3677"></A>This <EM CLASS="Emphasis">Virtual Machine Specification for the Java Card Platform, Version 2.2.2</EM> is the key to providing binary portability. One way of understanding what this specification does is to compare it to its counterpart in the Java platform. The Java virtual machine specification defines a Java virtual machine as an engine that loads Java class files and executes them with a particular set of semantics. The class file is a central piece of the Java architecture, and it is the standard for the binary compatibility of the Java platform. The <EM CLASS="Emphasis">Virtual Machine Specification for the Java Card Platform, Version 2.2.2</EM> also defines a file format that is the standard for binary compatibility for the Java Card platform: the CAP file format is the form in which software is loaded onto devices which implement a Java Card virtual machine.</P><H2 CLASS="Head1"><A NAME="pgfId-65"></A><DIV><HR ALIGN=left SIZE=6 WIDTH=15% noshade></DIV>1.2 The <A NAME="marker-3901"></A>Java Card Virtual Machine</H2><P CLASS="Paragraph"><A NAME="pgfId-2179"></A>The role of the Java Card virtual machine is best understood in the context of the process for production and deployment of software for the <A NAME="marker-3902"></A>Java Card platform. There are several components that make up a Java Card system, including the Java Card virtual machine, the Converter for the Java Card platform ("Java Card Converter"), a terminal installation tool, and an installation program that runs on the device, as shown in <A HREF="JCVM01intro.html#60790" CLASS="XRef">FIGURE 1-1</A> and <A HREF="JCVM01intro.html#31924" CLASS="XRef">FIGURE 1-2</A>.</P><BR>⌨️ 快捷键说明
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