The difference between JRE and JDK is detailed

Jdk

The JDK is the core of the entire Java system, including the Java Runtime Environment (Java Runtime envirnment), a stack of Java tools and a Java-based class library (Rt.jar). No matter what Java application Server is in essence a version of the JDK is built in. The most mainstream JDK is the JDK that Sun releases, and many companies and organizations, in addition to Sun, have developed their own JDK, such as the Jrocket of IBM's Jdk,bea company, the JDK developed by the GNU organization, and so on. IBM's JDK contains JVM (Java Virtual Machine) that is much more efficient than the JVM contained in the Sun JDK. The Jrocket, which runs on the x86 platform, is also much better at the server than the Sun JDK. But anyway, we need to get the sun JDK first.

JDK typically has three versions: SE (J2SE), Standard Edition, Standard Edition, is one of our usual versions of EE (Java ee), enterpsise edtion, Enterprise Edition, use this JDK to develop Java EE applications, ME (J2ME), Micro Edtion, the Java Application Java Development tool (JDK) for mobile devices, embedded devices, is the development environment that many Java experts have originally used. Although many programmers have used 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 are built, tested, and documented. Its core Java API is a predefined class library that developers need to use to access the functionality of the Java language. The Java API includes important language constructs as well as basic graphics, network, and file I/O. In general, the non-I/O portions of the Java API are the same for all platforms running Java, while the I/O portion is only implemented in the common Java environment.

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

Javac:java the compiler to convert the Java source code to byte code.

Java:java interpreter to execute 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 from Java source and description statements.

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

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

Javap:java the disassembler, showing the accessibility features and data in the compiled class file, while displaying the meaning of the byte code.

Jre

JRE (Java Runtime Environment,java running environment), a collection of environments necessary to run Java programs, including JVM standard implementations and Java core class libraries. Is the sun's product, which includes two parts: Javaruntimeenvironment and Javaplug-injavaruntimeenvironment (JRE) is the Java platform on which applications can be run, tested, and transferred. 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 assistive software--javaplug-in--to run the applet in the browser. J2re is JAVA2 Runtime environment, the Java Runtime Environment, sometimes referred to as JRE. If you only need to run a Java program or applet, download and install it. Download the JDK if you want to develop your own Java software. Note that there is a JRE attached to the JDK. Notice that because Microsoft does not support Java fully, do not use IE's own virtual machine to run applets, be sure to install a JRE or JDK.