Differences in concepts of JDK, J2EE, j2se, and J2EE

Differences in concepts of JDK, J2EE, j2se, and J2EE

1. JDK is a Java development toolkit, which is equivalent to a Java library function. Is to compile and run JavaProgram. So what is JDK? What is the difference between it and SDK? The SDK is the abbreviation of software development kit ". This is a widely used term. It can be said that the collection of documents, examples, and tools used to assist in the development of a certain type of software can be called "sdks "; JDK = Java SDK (if Microsoft C # is used for development, C # SDK is required). JDK is the core of Java, including the Java Runtime Environment (Java runtime envirnment), a bunch of Java tools and Java base class libraries (RT. jar ). No matter what Java application server is actually built into a certain version of JDK. Therefore, mastering JDK is the first step to learn java well. The most popular JDK is the JDK released by Sun. In addition to sun, many companies and organizations have developed their own JDK, such as JDK developed by IBM and jrocket of Bea, and JDK developed by GNU. Among them, the JVM (Java Virtual Machine) Running Efficiency of ibm jdk is much higher than that of Sun JDK. The jrocket running on the X86 platform is much more efficient on the server than Sun JDK. However, we still need to Master Sun JDK first.
Java 2 Enterprise Edition is a Java Enterprise Edition for enterprise-level application service development.
J2se is Java 2 Standard Edition is Java Standard Edition for standard application development
Java 2 Micro Edition is a Micro Edition of Java, which is often used for development on mobile phones.
J2EE, j2se, and j2se provide different services for different Java usage, that is, provide different types of class libraries. J2EE (Java 2 Enterprise Edition) for enterprise network applications, j2se (Java 2 Standard Edition) for general PC applications, and j2se (Java 2 Micro Edition) for embedded devices and consumer appliances) three versions. For beginners, they all start with j2se.
2. Differences between J2EE and j2se
J2EE adds a series of enterprise-level application programming interfaces on the basis of j2se. J2EE contains many technologies! Among them, you are familiar with JSP, Servlet, JDBC, jme and other 13 technology!
J2EE is mainly used for B/S structure applications! That is to say, it is based on browsers and servers! It Supports distributed components and multiple containers at the same time. ;
J2se is the most basic Java program running toolkit, including the most basic Java class libraries, such as Java. lang. string is one of the basic class libraries. The j2se package is sufficient for developing desktop applications (the so-called C/S structure). For example, eclipse is developed by it, which is equivalent to Microsoft's C #; in fact, J2EE is equivalent to Microsoft's ASP. net, which is specially used for web development. The package contains the j2se package. In addition, it provides some class libraries related to Web Development (JSP and Servlet interfaces and APIs ), for example, the httpservletrequest object is one of its class libraries, and j2se is used to develop desktop applications. Therefore, you do not need to use these HTTP objects (enterprise-level development of J2EE on the internet, dizzy! Isn't it just the development of a website (or the so-called B/S structure, when it's really scaring a large number of beginners (including me ^-^ )!); Similarly, mobile apps may be a little simpler than normal desktop applications, so there is no need to use so many class libraries, that is, the so-called Java service (which is just a basic class, the C language is also called the C service). Therefore, the so-called j2se actually removes some class libraries from j2se, it becomes a development platform for micro-mobile apps.
3. What is J2EE?
J2EE is a standard proposed by Sun. The product that complies with this standard is called "implementation". The J2EE development package of sun you downloaded has such an "implementation ", JBoss, WebLogic, and WebSphere are all "implementations" of the J2EE standard ". Because JBoss, WebLogic, and WebSphere have J2EE APIs, sun's J2EE implementation is not required.
4. Differences between J2EE SDK and j2sdkee
The J2EE SDK and j2sdkee can be regarded as the same thing. The official name is the J2EE SDK. J2eesdk is JDK. This is the Enterprise Java Bean (Enterprise Java Bean, Enterprise Edition JavaBean-the so-called Enterprise JavaBean. To put it bluntly, when developing a web project, java classes written in the background-do you know if you can understand this? Ah! Many concepts in Java are very simple, but they do not need to be interpreted in easy-to-understand languages. They have to take the Enterprise's Mark and make Java as mysterious as the legendary Java island !) Required.
5. Do I still need to install j2se SDK if I have installed J2EE SDK?
When you download j2ee1.4 on Sun's website, there are two download packages, one of which is the complete j2ee1.4 SDK package (all in one), including J2EE server, j2se, sample, API Doc; j2EE contains almost everything in j2se-there is a JDK in J2EE. The LIB below it is as big as the Lib below j2se (in the same version), but the JRE is not big, because J2EE is much more than j2se, such as Java. servlet. *, Java. servlet. HTTP..
J2EE is something that allows you to develop J2EE specification. for a Web server, do not install J2EE. You only need to install a JRE (not even j2se) and a Servlet Engine (such as Tomcat.
Take a look at the following:
J2se = JDK = bin + demo + include + JRE + lib + src.rar/Sun's official jdk1.4.2
J2EE = JDK +... // The JDK here is different from the JDK File above. The reason is as mentioned above.
The other is a separate J2EE server. You must install the j2se SDK before installation.
After installation, you must set the java_home, j2ee_home, and classpath environment variables before running the J2EE server.

To facilitate developers, Sun divides Java into four platforms: j2se (Java 2 Standard Edition), J2EE (Java 2 Enterprise Edition), Java 2 Micro Edition (Java 2 Micro Edition), and Java card. J2se is the foundation of all Java technologies. No matter what platform Java applications developers need to develop, they must first learn from j2se. The J2EE Technology focuses on Enterprise Server applications. Mainly for embedded systems, such as mobile phones and PDAs. Sun also provides the free j2e-wireless toolkit for mobile app development. Java card technology is used to develop applications that can be implanted into IC smart cards.