Java JDK, JRE, JVM

JDK: The JDK is used as the Java SDK for building applications, applets, and components that run on the Java platform.

Includes the Java Runtime Environment (Java Runtime Envirnment), a stack of Java tools (JAVAC/JAVA/JDB, etc.), and a Java-based class library (that is, the Java API includes Rt.jar).

　　　　The JDK is generally available in three versions : SE (J2SE), Standard Edition, standards, is a version of the EE we typically use, Enterpsise edtion, Enterprise Edition, using this JDK to develop the Java EE application, ME (J2ME), Micro edtion,

Java Application Java Development tools (JDK), primarily for mobile devices and embedded devices, are the first development environments 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 and basic shapes,

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.

JRE: JRE (Java Runtime Environment,java Runtime Environment), which is the Java platform. All Java programs must be run under the JRE. The JDK tool is also a Java program and requires a JRE to run. To maintain the independence and integrity of the JDK,

The JRE is also part of the installation during the installation of the JDK. Therefore, in the JDK installation directory, there is a directory named JRE, which is used to store the JRE file.

JVM: Java mechinal (Java Virtual machine). The JVM is part of the JRE, a fictional computer that is implemented by simulating various computer functions on a real computer. The JVM has its own complete hardware architecture,

such as processor, stack, register, etc., also have the corresponding instruction system. The main task of the JVM is to interpret its own instruction set (that is, bytecode) and map it to the local CPU's instruction set or system call to the OS. The Java language is run across platforms,

In fact, different operating systems, using different JVM mapping rules, so that it is independent of the operating system, the completion of cross-platform. The JVM does not care about the upper Java source files, it only focuses on the class file generated by the source file.

The composition of the class file includes the JVM instruction set, the symbol table, and some subsidy information.

Java JDK, JRE, JVM