Shulou(Shulou.com)06/02 Report--

This article mainly introduces the meaning of JDK and JRE, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

First, let's look at the meaning of JDK and JRE:

JDK is the core of the entire Java, including the Java runtime environment (Java Runtime Envirnment), a bunch of Java tools, and Java-based class libraries (rt.jar). No matter what Java application server is actually built-in a certain version of JDK. The most mainstream JDK is JDK released by Sun. In addition to Sun, many companies and organizations have developed their own JDK, such as JDK,BEA Jrocket developed by IBM, JDK developed by GNU and so on. Among them, the JVM (Java Virtual Machine) contained in the JDK of IBM is much more efficient than the JVM contained in Sun JDK. Jrocket, which runs exclusively on x86 platform, is much more efficient on the server side than Sun JDK. But in any case, we still need to master Sun JDK first.

JDK generally has three versions: SE (J2SE), standard edition, Standard Edition, is a version we usually use EE (J2EE), enterpsise edtion, Enterprise Edition, using this JDK to develop J2EE applications, ME (J2ME), micro edtion, java applications mainly used on mobile devices, embedded devices Java development tools (JDK) is the development environment originally used by many Java experts. Although many programmers have used third-party development tools, JDK is still regarded as an important tool for Java development. JDK consists of a standard class library and a set of Java utilities that build, test, and document. Its core Java API is a number of predefined class libraries that developers need to access the functions of the Java language. Java API includes some important language structures as well as basic graphics, networks and files. In general, the non-Imax O part of Java API is the same for all platforms running Java, while the Imax O part is only implemented in a generic Java environment.

As a JDK utility, there are seven main programs in the tool library.

◆ Javac:Java compiler, which converts Java source code into bytecode.

The ◆ Java:Java interpreter executes the Java application bytecode directly from the class file.

◆ appletviewer: Mini Program browser, a Java browser that executes Java Mini Program on HTML files.

◆ Javadoc: generate HTML documents according to Java source code and description statements.

The ◆ Jdb:Java debugger, which can execute the program line by line, set breakpoints, and check variables.

◆ Javah: generate a C procedure that can call a Java procedure, or create a header file for a C procedure that can be called by a Java program.

◆ Javap:Java disassembler, which displays accessible functions and data in compiled class files, as well as the meaning of bytecode.

JRE (Java Runtime Environment,Java runtime environment), a collection of environments necessary to run JAVA programs, including JVM standard implementation and Java core class libraries. Is a product of Sun and consists of two parts: JavaRuntimeEnvironment and JavaPlug-inJavaRuntimeEnvironment (JRE) are Java platforms on which applications can be run, tested, and transferred. It includes the Java virtual machine, Java platform core classes and support files. It does not include development tools-compilers, debuggers, and other tools. JRE needs auxiliary software-- JavaPlug-in-- to run applet.J2RE in a browser. Applet.J2RE is Java2 Runtime Environment, the Java runtime environment, sometimes referred to as JRE. If you only need to run the Java program or Applet, download and install it. If you want to develop your own Java software, please download JDK. JRE. JRE is attached to JDK. Note that as Microsoft does not fully support Java, please do not use the virtual machine that comes with IE to run Applet, be sure to install a JRE or JDK.

The role of JDK and JRE in starting the application server:

When I first came into contact with Java, I thought the Java virtual machine was troublesome. I didn't understand the difference between JRE and JDK. Later it became clear that JRE is a running environment and JDK is a development environment. So you need JDK to write Java programs and JRE to run Java programs. JDK already contains JRE, so you can run Java programs normally when JAVA_HOME is set to the path of JDK, but JDK contains a lot of content that has nothing to do with running, so it is not necessary to install JDK to run ordinary Java programs.

But with Eclipse, there is a question, why does this development environment JRE work properly? In fact, the Java compiler is embedded in Eclipse and is fully compatible with javac in JDK, so you can compile Java programs directly without using JDK.

When learning J2EE, I don't understand why Tomcat and Apusic can be started with JRE and Weblogic can only be started with JDK. The reason is that both Tomcat and Apusic 4 already include a source code compiler, while Weblogic does not include this compiler package.

So why do you need a compiler? Because in WEB applications, JSP files need to be converted to Servlet, and this Servlet file also needs to be compiled into class files that can be executed on JRE, it is necessary to provide JDK with the ability to compile, and set JAVA_HOME to the path of JDK.

What about the new Apusic 5. 0? In order to give you the flexibility to adjust the version of JVM, this version no longer provides its own Java compiler, but compiles JSP through the user-installed JDK, which is why Apusic 5.0 must be started through JDK.

Thank you for reading this article carefully. I hope the article "what is the meaning of JDK and JRE" shared by the editor will be helpful to you. At the same time, I also hope you will support us and pay attention to the industry information channel. More related knowledge is waiting for you to learn!

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