The name of the Java platform for the enterprise has been simplified. Formerly, the platform was known as Java 2 Platform, Enterprise Edition (J2EE), and specific versions had "dot numbers" such as J2EE 1.4. The "2" has been dropped from the name, as has the minor revision number. So the next version of the Java platform for the enterprise is Java Platform, Enterprise Edition 5 (Java EE 5).
 it come from http://java.sun.com/javaee/overview/faq/javaee_faq.jsp#diff

     摘要: 1. SDK(Software Develop Kit，软件开发工具包)，用于帮助开发人员的提高工作效率。各种不同类型的软件开发，都可以有自己的SDK。Windows有Windows SDK，DirectX 有 DirectX 9 SDK，.NET开发也有Microsoft .NET Framework SDK。JAVA开发也不含糊，也有自己的Java SDK。
2. JDK，Java SDK最早叫Java Software Develop Kit，后来改名为JDK，即Java Develop Kit。JDK作为Java开发工具包，主要用于构建在Java平台上运行的应用程序、Applet 和组件等。
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