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JDK (Java Development Kit) is a product for Java developers, is the core of Java, including Java runtime environment JRE, Java based tools and Java class libraries. Java Runtime Environment (JRE) is a collection of programs that must be run JAVA environment, including JVM Java core libraries and standard implementation. JVM is an acronym for Java Virtual Machine (Java Virtual Machine), the entire core java achieve cross-platform part, be able to run software programs in Java writing.
In the history of computer development language, the language of which has never been as supported by so many manufacturers like Java, there are so many development tools.
JDK（Java Development Kit）
JDK is the Java Development Kit, is a Sun Microsystems product for Java developers is.
JDK contains the JRE, there is a directory called jre in JDK installation directory, there are two folders bin and lib, where you can think of in the bin is jvm, lib is in the library jvm needed for the work while jvm lib and up and called jre.
JAVA JDK is the core, including the Java Runtime Environment JRE (Java Runtime Envirnment), a bunch of Java tools (javac / java / jdb, etc.) and Java-based libraries (Java API that is included rt.jar).
①SE (J2SE), standard edition, Standard Edition, is a version we usually use, from JDK 5.0, renamed Java SE.
②EE (J2EE), enterprise edition, Enterprise Edition, using this JDK develop J2EE applications from JDK 5.0, renamed Java EE.
③ME (J2ME), micro edition, mainly for java applications on mobile devices, embedded devices, from JDK 5.0, renamed Java ME.
Pyramid structure JDK = JRE + JVM + other run Java programs typically require the user's computer to install the JRE (Java Runtime Environment); no jre, java program can not run; without java program, jre will become useless.
Pyramid structure JDK = JRE + JVM + other run Java programs typically require the user's computer to install the JRE (Java Runtime Environment); no jre, java program can not run; without java program, jre will become useless.
Java Runtime Environment（JRE）
It is run based on programs written in the Java language indispensable operating environment. It is also through, Java developers were able to develop their own program will be released to the hands of users, allowing users to use.
RE contains the Java virtual machine (JVM), runtime class libraries, and Java application launcher, which is a necessary component to run Java programs.
And well-known different JDK, JRE Java Runtime Environment is not a development environment, it does not contain any development tools (such as compilers and debuggers), but the user to use a Java program for.
JVM（java virtual machine）
We often say that the java virtual machine, which is the core part of the whole java cross-platform, all the java program will first be compiled into class files .class of this class file can be executed on a virtual machine.
That class does not directly correspond to the operating system of the machine, but indirectly through the virtual machine operating system to interact with the virtual machine will perform the procedure explained to the local system.
JVM not only to perform in class, because in the interpretation of class when JVM needs to be called to explain the library lib need, and jre lib contains libraries.
JVM mask information associated with a particular operating system platform, so that only the Java program to generate object code (bytecode) running in the Java virtual machine can run without modification on multiple platforms.