下面是甲骨文的一个简单回应 http://docs.oracle.com/javase/7/docs/technotes/guides/

Java SE运行环境(JRE)

JRE提供了运行用Java编程语言编写的applet和应用程序所需的库、Java虚拟机和其他组件。这个运行时环境可以与应用程序一起重新分发，使它们独立。

Java SE开发套件(JDK)

JDK包括JRE和命令行开发工具，如编译器和调试器，这对于开发applet和应用程序是必要的或有用的。

下面是甲骨文的一个简单回应 http://docs.oracle.com/javase/7/docs/technotes/guides/

Java SE运行环境(JRE)

JRE提供了运行用Java编程语言编写的applet和应用程序所需的库、Java虚拟机和其他组件。这个运行时环境可以与应用程序一起重新分发，使它们独立。

Java SE开发套件(JDK)

JDK包括JRE和命令行开发工具，如编译器和调试器，这对于开发applet和应用程序是必要的或有用的。

从调试的角度来看，有一个不同之处:

要调试到Java系统类，如String和ArrayList，你需要一个特殊版本的JRE，它是用“调试信息”编译的。JDK中包含的JRE提供了这些信息，但常规的JRE没有。常规JRE不包含此信息，以确保更好的性能。

什么是调试信息?以下是这篇博文的简要解释:

Modern compilers do a pretty good job converting your high-level code, with its nicely indented and nested control structures and arbitrarily typed variables into a big pile of bits called machine code (or bytecode in case of Java), the sole purpose of which is to run as fast as possible on the target CPU (virtual CPU of your JVM). Java code gets converted into several machine code instructions. Variables are shoved all over the place – into the stack, into registers, or completely optimized away. Structures and objects don’t even exist in the resulting code – they’re merely an abstraction that gets translated to hard-coded offsets into memory buffers. So how does a debugger know where to stop when you ask it to break at the entry to some function? How does it manage to find what to show you when you ask it for the value of a variable? The answer is – debugging information. Debugging information is generated by the compiler together with the machine code. It is a representation of the relationship between the executable program and the original source code. This information is encoded into a pre-defined format and stored alongside the machine code. Many such formats were invented over the years for different platforms and executable files.

JRE即Java运行时环境。它是运行已编译Java程序所需的所有东西的包，包括Java虚拟机(JVM)、Java类库、Java命令和其他基础设施。但是，它不能用于创建新程序。

JDK是Java Development Kit，是Java的全功能SDK。它拥有JRE所拥有的一切，还包括编译器(javac)和工具(如javadoc和jdb)。它能够创建和编译程序。

通常，如果你只关心在电脑上运行Java程序，你只会安装JRE。这就是你所需要的。另一方面，如果您计划进行一些Java编程，则需要安装JDK。

有时，即使您不打算在计算机上进行任何Java开发，仍然需要安装JDK。例如，如果您正在使用JSP部署web应用程序，那么从技术上讲，您只是在应用服务器中运行Java程序。那么为什么需要JDK呢?因为应用服务器将JSP转换为Java servlet，并且需要使用JDK来编译servlet。我相信还有更多的例子。

上面的答案(Pablo)是非常正确的。这只是额外的信息。

顾名思义，JRE是一个环境。它基本上是一堆包含java相关文件的目录，即:

bin/ contains Java's executable programs. The most important is java (and for Windows, javaw as well), which launches the JVM. There are some other utilities here as well, such as keytool and policytool. conf/ holds user-editable configuration files for Java experts to play with. lib/ has a large number of supporting files: some .jars, configuration files, property files, fonts, translations, certs, etc. – all the "trimmings" of Java. The most important is modules, a file that contains the .class files of the Java standard library. At a certain level, the Java standard library needs to call into native code. For this purpose, the JRE contains some .dll (Windows) or .dylib (macOS) or .so (Linux) files under bin/ or lib/ with supporting, system-specific native binary code.

JDK也是一组目录。它是JRE的超集，增加了一些功能:

Bin /已经被开发工具放大了。其中最重要的是javac;其他包括jar、javadoc和jshell。 添加了jmods/，用于保存标准库的JMOD文件。这些文件允许标准库与jlink一起使用。

通俗地说:JDK是祖父，JRE是父亲，JVM是他们的儿子。 [即JDK > JRE > JVM]

JDK = JRE +开发/调试工具 JRE = JVM + Java包类(如util, math, lang, awt,swing等)+运行时库。 JVM =类装入器系统+运行时数据区+执行引擎。

换句话说，如果你是一个Java程序员，你将需要JDK在你的系统中，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，这个包不会有JDK。

JVM:

The Java Virtual Machine (JVM) is the virtual machine that run the Java bytecodes. The JVM doesn't understand Java source code, that's why you compile your *.java files to obtain *.class files that contain the bytecodes understandable 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运行环境(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开发工具包(JDK)

JDK是JRE的超集，包含JRE中的所有内容，以及开发小程序和应用程序所需的编译器和调试器等工具。

注意，Oracle并不是唯一提供JDK的公司。

JIT编译过程(来源:Oracle文档)