My Java Road
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* This article is first in BBS.Bluegem.org Java District
* I email: chenfei@sohu.com
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In the initial contact, Java, was confused by a large pile. What Java, Java2, J2se, J2EE, J2ME, JavaBeans, EJB ..., what is it? Coast!
First clarify something, since the launch of JDK 1.2, Sun has renamed Java as Java2, and the Java mentioned now means Java2.
The reason why Java is so mysterious, because Java is both a language and a platform, or a architecture. If you don't understand the Java platform, you can't understand Java. Regrettably, few people can explain the Java platform in depth.
If you open the Java platform, just as a programming language, Java is different from the traditional language in grammar and programming ideas (referring to Coding). Java has the benefits of pure object-oriented, optimized memory management models, specific details, I write is also Copy & Paste, nothing.
I will talk about the Java platform according to my understanding.
First, the compiled Java program is not directly running binary code on a particular operating system, but a so-called bytecode. To see a computer installed as a Java VM as a virtual machine, bytecode can only run on this virtual machine. What is not important as the real hardware and operating system. what? Have you heard of a virtual machine? That hurriedly turned out "Computer Principles", I can't talk about such a deep stuff. In fact, I don't understand, as long as I know that the Java language compiled in WIN, * NIX or Mac OS must be settled enough to make a java virtual machine.
Speaking here, the heart is already conceived that since Java writes the program is running on the Java virtual machine, then the same compiled Java can run on any Java virtual machine, not
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What is the hardware of what is the operating system under the heart Java virtual machine. This is the "once written, run" characteristics in Sun has been bragging. It seems that it is natural to introduce it, see the importance of the basic course in the university, haha!
You can continue after this.
The basis of the Java architecture is J2SE (Java 2 Platform, Standard Editions), as the name suggests, standard version. J2SE The bottom is the JRE (Java runtime environment), JRE provides components including Java API, Java virtual machines, and other support Applets and Java applications. That is to say, JRE is installed, you can run various programs written by Java. With JRE, you can't develop Java programs. If you want to develop Java programs, you need JDK (Java development pack), corresponding to SDK in Win. JDK is naturally included in COMPILER and DEBUGER. For details, refer to http://java.sun.com/j2se/overview.html, the official website is very clear.
J2EE (Java 2 Platform, Enterprise Edition), relative J2SE, very clearly J2EE is serving business. J2EE is a supercoming of J2SE and provides a platform for business operations. This use of Java technology on this platform has many advantages: Easy to develop, cross-platform, compatible with other applications such as databases, CORBA, easy to implement middleware. The technical means of achieving EJB (Enterprise Javabeans), Java Servlets API, JSP (JavaServer Pages) and XML. Let's explain it.
Java Application: Like a normal Windows application or LINUX ELF application, "executable" written in Java language. The ignometer means that it can only run on the Java virtual machine, and cannot run on a low level virtual machine.
Applet: The so-called "Java applet" is confused? In fact, I didn't understand what it was in the first time. Applet is a special program that can only be run in a browser that supports applet. If the browser does not support, then she can only lament from ancient red intense. Fortunately, most browsers now support the applet.
Servlet and JSP:
The difference between CGI and server-side scripts will be taught before explaining JSP and servlet. Both CGI and server-side scripts implement dynamic web pages, CGI is a special executable running on the server side, using C to write a CGI; the server-side script is an explanation of the scripting language, not executable. Her operation requires WWW server support, such as the ASP, ASP.NET, APATCH supporting PHP, supported by IIS.
The servlet is a CGI running on the Java platform, which is a special procedure for compiling Java. JSP is the scripting language that requires WWW server support.
The JDBC: Connecting the Database on the Java platform is similar to ODBC.
EJB (Enterprise Javabeans): I don't quite understand anything now. I only know that it is a high reusable program. The main role is to hide the heterogeneous system. Provide independent programming interfaces, JSP and Servlet programmers do not have to be available to the upper JSP and Servlet
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What kind of system is in the end of the heart EJB.
I understand the Java platform:
The core of Java is cross-platform. The complex system is finely divided into a multi-layer, and the heterogeneity characteristics of the bottom layer are shielded, providing a unified access interface for the high layer. This model can refer to the seven-layer protocol model of the network.
For a single machine, such as the machine running Windows2000 on the Pentium, running Linux machines on Pentium, RS60000 running AIX machine is different platforms. Sun has developed a corresponding version of Java virtual machine for different operating systems, so that the same Java application does not have to recompile to run on any platform installed in the Java virtual machine.
It is slightly more complicated to the network environment. The traditional three-story model does not speak, you don't understand the information. The model of the Java platform is a bit different. Please refer to http://java.sun.com/j2ee/images/appmodel.jpg. The same access method is provided by EJB for different databases, shielding the isomer of the database. Such JSP and Servlet's programmers can do not have to
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The heart visits the details of different databases, focusing on the algorithm.
