Relationship among JDK, JRE, and JVM

Relationship among JDK, JRE, and JVM

JDK (Java Development Kit) is a product for Java developers. It is the core of Java, including the Java Runtime Environment JRE, Java tools, and Java base class libraries. Java Runtime Environment (JRE) is a set of environments required to run JAVA programs, including JVM standard implementation and Java core class libraries. JVM is the abbreviation of Java Virtual Machine (java Virtual Machine). It is the core of cross-platform implementation in Java and can run software programs written in Java.

In the history of computer development languages, no language has ever been supported by so many vendors as Java, and there are so many development tools.

JDK (Java Development Kit)

JDK is a Java development kit and a product developed by Sun Microsystems for Java developers.

JDK contains JRE. Under the JDK installation directory, there is a directory named jre, which contains two folders bin and lib. Here we can think that the bin contains jvm, lib is the class library required for jvm work, while jvm and lib are called jre.

JDK is the core of JAVA, including the Java Runtime Environment JRE (Java Runtime Envirnment) and a bunch of Java tools (javac/java/jdb) and Java-based class libraries (that is, Java APIs include rt. jar ).

① SE (J2SE), standard edition, and standard edition are a common version. They have been renamed Java SE since JDK 5.0.

② EE (J2EE), enterprise edition, and enterprise edition, used this JDK to develop J2EE applications, and changed its name from JDK 5.0 to Java EE.

③ ME (j2e-micro edition) is mainly used for java applications on mobile devices and embedded devices. It has been renamed Java ME since JDK 5.0.

The pyramid structure JDK = JRE + JVM + other Java programs generally require the user's computer to install the JRE Environment (Java Runtime Environment); without jre, java programs cannot run; without java programs, jre is useless.

Java Runtime Environment (JRE)

It is an indispensable runtime environment for running programs written based on the Java language. It also enables Java developers to publish their own programs to users for use.

RE contains Java virtual machine (JVM), runtime class libraries and Java application launcher, which are necessary components for running Java programs.

Different from the well-known JDK, JRE is a Java Runtime Environment, not a development environment, so it does not contain any development tools (such as compilers and debuggers ), only for users who use Java programs.

JVM (java virtual machine)

Java Virtual Machine (VM) is the core of cross-platform java Implementation. All java programs are first compiled. class files, which can be executed on virtual machines.

That is to say, the class does not directly correspond to the operating system of the machine, but indirectly interacts with the operating system through the Virtual Machine. The virtual machine interprets the program to the local system for execution.

Only the JVM cannot be executed as a class, because when interpreting the class, the JVM needs to call the library lib required for interpretation, and the jre contains the lib class library.

JVM shields information related to the specific operating system platform, so that Java programs only need to generate the target code (bytecode) that runs on the Java Virtual Machine ), it can be run on multiple platforms without modification.

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