The differences between the two JRE and the JRE and the JDK in eclipse

Classification:

—————————— differentiate between the two JRE ———————-in eclipse

(Eclipse is also an ordinary Java program, so there must be a JRE as the operating environment.) If you do not have any JRE (or JDK) installed on your machine, then clicking Eclipse.exe will make an error saying that the JRE could not be found. You can install a JRE at this point, or copy the JRE directory directly to the Eclipse installation directory.

You can specify different JRE versions for your project in each project in eclipse, such as a project using JDK1.4 compilation, and B projects using JDK1.5 compilation. This JDK version is not directly related to the Eclipse run JRE.
If the-VM parameter is configured in the Eclipse.ini, then the JRE specified by this parameter is used, otherwise the JRE folder is checked for the Eclipse installation directory, if any, the JRE is used, otherwise the system is searched for the installed JRE, and if it is not found, an error is given.

——————————— the difference between the JRE and the JDK ——————————————-

If you install the JDK, you actually have the JRE installed,

The JDK is the one you use to compile your Java program (JAVAC).
And the JRE is the (Java) you use to run Java programs.

Installing the JDK found that there were two sets of JRE on the computer because the tools in the JDK were written almost in Java, and so were Java applications, so it was necessary to use the tools attached to the JDK to develop Java programs and also to attach a set of JRE itself.

Eclipse-window-preferences-java-installed JRES\ADD\JDK

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Jdk

The JDK is the core of the entire Java, including the Java Runtime (Java Runtime Envirnment), a stack of Java tools, and a Java-based class library (Rt.jar). No matter what Java application Server is essentially a version of the JDK built in. The most mainstream JDK is Sun's JDK, and many companies and organizations have developed their own JDK in addition to sun, such as the Jrocket of JDK,BEA company developed by IBM, the JDK developed by the GNU organization, and so on. Where IBM's JDK contains a JVM (Java Virtual machine) that runs much more efficiently than the JVM contained in the Sun JDK. The jrocket running on the x86 platform is also much more efficient than the sun JDK on the service side. But in any case, we need to get the sun JDK in the first place.

The JDK is generally available in three versions: SE (J2SE), Standard Edition, standards, is a version of the EE that we usually use, Enterpsise edtion, Enterprise Edition, using this JDK to develop the Java EE application, ME (J2ME), Micro Edtion, a Java Application Java development tool (JDK) used primarily for mobile devices and embedded devices, is the first development environment used by many Java experts. Although many programmers already use third-party development tools, the JDK is still considered an important tool for Java development. The JDK consists of a standard class library and a set of Java utilities that build, test, and build documents. Its core Java APIs are predefined class libraries that developers need to use to access the capabilities of the Java language. The Java API includes some important language constructs as well as basic graphics, network and file I/O. In general, the non-I/O portion of the Java API is the same for all platforms running Java, while the I/O part is only implemented in a common Java environment.

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

Javac:java compiler to convert Java source code into bytecode.

The Java:java interpreter executes the Java application byte code directly from the class file.

Appletviewer: Applet browser, a Java browser that executes Java applets on HTML files.

Javadoc: Generates HTML documents According to Java source code and description statements.

Jdb:java debugger, you can execute the program line by row, set breakpoints and check variables.

Javah: Generates a C procedure that can invoke a Java procedure, or a header file that can be called by a Java program.

The Javap:java disassembler, which displays the accessible functionality and data in the compiled class file, shows the meaning of the byte code.

Jre

JRE (Java Runtime Environment,java Runtime Environment), a collection of environments necessary to run Java programs, including the JVM standard implementation and the Java Core Class library. are Sun's products, including two parts: Javaruntimeenvironment and Javaplug-injavaruntimeenvironment (JRE) are the Java platforms on which applications can be run, tested, and transmitted. It includes Java virtual machines, Java platform core classes, and supporting files. It does not contain development tools-compilers, debuggers, and other tools. The JRE requires auxiliary software--javaplug-in--to run applets in the browser. J2re is the JAVA2 runtime environment, the Java Runtime Environment, sometimes referred to as the JRE. If you only need to run a Java program or applet, download and install it. If you are developing your own Java software, download the JDK. The JRE is included with the JDK. Note Because Microsoft does not have complete support for Java, do not use IE's own virtual machine to run applets, be sure to install a JRE or JDK.

The differences between the two JRE and the JRE and the JDK in eclipse