Java Platform Editions

These two aspects of the Java Platform are the Java Runtime Environment (JRE)and the Java Development Kit (JDK).
The JRE provides the operating system the means to run Java programs.
The JDK is a collection of tools used by a programmer to create Java applications. The JDK includes a compiler that makes Java source code readable by your computer.
The JRE is contained within the JDK i.e., if you are a developer and download the JDK, you will also get the JRE and be able to run Java programs.
The JDK is embedded in the various editions of the Java Platform, all of which include the JDK, the JRE, and a set of Application Programming Interfaces (APIs) that help developers write programs. These editions include Java Platform, Standard Edition (Java SE) and Java Platform, Enterprise Edition (Java EE).
Oracle also provides a Java version for developing applications for mobile devices, called Java Platform, Micro Edition (Java ME).
Java both the JRE and the JDK - is free and always has been. The Java SE edition, which includes the set of APIs for development, is also free, but the Java EE edition is fee-based.

The JRE or Runtime Environment

When your computer continually pesters you with a notice "Java Update Available," this is the JRE the environment required to run any Java application.
Whether you're a programmer or not, you likely need the JRE unless you are a Mac user or you have decided to avoid applications that use it.
Because Java is cross-platform compatible which just means that it works on any platform including Windows, Macs and mobile devices it is installed on millions of computers and devices around the world.
It has become the target of hackers and has been vulnerable to security risks, which is why some users choose to avoid it.

The Java Standard Edition (Java SE) is designed for building desktop applications and applets.
These applications typically serve a small number of users at one time, i.e. they are not intended to be distributed across a far-flung network.

The Java Enterprise Edition (Java EE) includes most of the components of the Java SE but is tailored for more complex applications to suit medium to large businesses.

Typically, the applications developed are server-based and focus on meeting the needs of multiple users at a time.

This edition provides higher performance than the Java SE and a range of enterprise-class services.

The Java Micro Edition is for developers who are creating applications for use on mobile (e.g., cell phone, PDA) and embedded devices (e.g., TV tuner box, printers).