JVM是Java虚拟机-它实际上运行Java字节码。

JRE是Java运行时环境——其中包含JVM，并且是运行Java程序所需要的。

JDK是Java开发工具包——它是JRE，但添加了javac(这是编译Java源代码所需的工具)和其他编程工具。

OpenJDK是一个特定的JDK实现。

另一个值得一提的方面是:

JDK (java开发工具包)

正如名称所示，您将需要它用于开发目的。

例如:一家软件公司会在他们的计算机中安装JDK，因为他们需要开发新的软件，其中包括编译和运行他们的Java程序。

因此我们可以说JDK = JRE + JVM。

JRE (java运行时环境)

运行Java程序需要它。你不能用它来编译Java程序。

例如:一个普通的计算机用户想要运行一些在线游戏，那么他的系统中就需要JRE来运行Java程序。

java虚拟机

你可能知道它运行字节码。它使Java平台独立，因为它执行你编译Java程序后得到的.class文件，而不管你是在Windows、Mac还是Linux上编译。

开放的JDK

就像我上面说的。现在JDK是由不同的公司制作的，其中一个是开源的，免费供公众使用的是OpenJDK，而其他一些是Oracle公司的jrocit JDK或IBM JDK。

然而，对于普通用户来说，它们可能都是一样的。

结论

如果你是一个Java程序员，你的系统中需要JDK，这个包将包括JRE和JVM，但如果你是一个喜欢玩在线游戏的普通用户，那么你只需要JRE，这个包中没有JDK。

换句话说，JDK是祖父，JRE是父亲，JVM是他们的儿子。

通俗来说:JDK = JRE +开发/调试工具，其中JDK是我们与Java一起工作的完整包，从创建编译到运行它。另一方面，JRE只是代码(字节码)的运行。

注意:-无论我们是安装JDK还是JRE, JVM都会与这两个包捆绑在一起，JVM是JIT编译器将字节代码转换为机器特定代码的部分。

只需阅读关于JDK、JRE、JVM和JIT的文章即可

JRE执行应用程序，但JVM逐行读取指令，因此它是解释器。

JDK = JRE +开发工具

JRE = JVM +库类

JVM

The Java Virtual Machine (JVM) is the virtual machine that runs the Java bytecodes. The JVM doesn't understand Java source code; that's why you need compile your *.java files to obtain *.class files that contain the bytecodes understood by the JVM. It's also the entity that allows Java to be a "portable language" (write once, run anywhere). Indeed, there are specific implementations of the JVM for different systems (Windows, Linux, macOS, see the Wikipedia list), the aim is that with the same bytecodes they all give the same results.

JDK和JRE

要解释JDK和JRE之间的区别，最好是阅读Oracle文档并参考图:

Java Runtime Environment (JRE) The Java Runtime Environment (JRE) provides the libraries, the Java Virtual Machine, and other components to run applets and applications written in the Java programming language. In addition, two key deployment technologies are part of the JRE: Java Plug-in, which enables applets to run in popular browsers; and Java Web Start, which deploys standalone applications over a network. It is also the foundation for the technologies in the Java 2 Platform, Enterprise Edition (J2EE) for enterprise software development and deployment. The JRE does not contain tools and utilities such as compilers or debuggers for developing applets and applications. Java Development Kit (JDK) The JDK is a superset of the JRE, and contains everything that is in the JRE, plus tools such as the compilers and debuggers necessary for developing applets and applications.

注意，Oracle并不是唯一提供jdk的公司。

OpenJDK

OpenJDK是JDK的开源实现，也是Oracle JDK的基础。Oracle JDK和OpenJDK之间几乎没有区别。

区别在这个博客中说明:

Q: What is the difference between the source code found in the OpenJDK repository, and the code you use to build the Oracle JDK? A: It is very close - our build process for Oracle JDK releases builds on OpenJDK 7 by adding just a couple of pieces, like the deployment code, which includes Oracle's implementation of the Java Plugin and Java WebStart, as well as some closed source third party components like a graphics rasterizer, some open source third party components, like Rhino, and a few bits and pieces here and there, like additional documentation or third party fonts. Moving forward, our intent is to open source all pieces of the Oracle JDK except those that we consider commercial features such as JRockit Mission Control (not yet available in Oracle JDK), and replace encumbered third party components with open source alternatives to achieve closer parity between the code bases.

JDK 11的更新

Donald Smith的一篇文章试图消除Oracle JDK和Oracle的OpenJDK之间的差异:https://blogs.oracle.com/java-platform-group/oracle-jdk-releases-for-java-11-and-later

正如@Alan Evangelista在评论中提到的，Java Web Start已被Oracle在Java SE 9中弃用，并在Java SE 11中删除。

JVM is abbreviated as Java Virtual Machine, JVM is the main component of java architecture. JVM is written in C programming language. Java compiler produce the byte code for JVM. JVM reading the byte code verifying the byte code and linking the code with the ibrary. JRE is abbreviated as Java Runtime Environment. it is provide environment at runtime. It is physically exist. It contain JVM + set of libraries(jar) +other files. JDK is abbreviated as Java Development Kit . it is develop java applications. And also Debugging and monitoring java applications . JDK contain JRE +development tools(javac,java)

OpenJDK是sun JDK的开源版本。Oracle JDK是Sun的官方JDK。