JDK JVM JRE

Often we interchange the terms JRE, JDK, and JVM. However, this misuse of terms can cause confusion in technical discussions. This document will attempt to offer a simplified explanation of each term and how they apply to our environments.
This document is intended for administrators of Oracle Forms application deployment. A basic understanding of Forms deployment concepts is recommended prior to utilizing this document. This document may also be useful to anyone using a JRE to deploy Java applets or administrators responsible for server-side JDK installations.

DETAILS

JRE - Java Runtime Environment

• 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.

The JRE is typically what is installed on a client machine. The JRE is sometimes correctly referred to as the Java Plug-in (JPI). Oracle Jinitiator is a JRE. It is a customized version of the Sun JRE based on version 1.3.1.x. A JRE is required on the end-user (client) machine in order to run Oracle Forms and several other Oracle applet based products.

JVM - Java Virtual Machine

• A Java Virtual Machine (JVM) is a set of computer software programs and data structures which use a virtual machine model for the execution of other computer programs. ...
• The JVM is distributed along with a set of standard class libraries which implement the Java API (Application Programming Interface). The virtual machine and API have to be consistent with each other and are therefore bundled together as the Java Runtime Environment (JRE). ...
• The JVM, which is the instance of the JRE (Java Runtime Environment), comes into action when a Java program is executed.

The JVM is not a distributable component, as described above. Therefore asking a customer to install a JVM is not exactly an accurate statement. It is the JRE that is installed, and the JVM represents a running instance of the JRE.

JDK - Java Development Kit

• The Java Development Kit (JDK) is a Sun Microsystems product aimed at Java developers. ...
• The JDK also comes with a complete Java Runtime Environment. It consists of a Java Virtual Machine and all of the class libraries that will be present in the production environment, as well as additional libraries only useful to developers, such as the internationalization libraries and the IDL libraries. ...
• Also included are a wide selection of example programs demonstrating the use of almost all portions of the Java API...

The JDK is what would typically be used on a developer's machine or server (e.g. within the Oracle Application Server or Developer Suite home). Although the JDK includes a JRE, it is an optional installation. For most Oracle customers calling to address Forms, Discoverer, or Apps issues on a client machine, there is no reason to install the JDK. It is the JRE that they should be downloading and installing. In the Oracle home's of most of our products, a JDK is included along with the JRE. These are intended mostly for server-side activities.
By using the correct terminology, we can help to reduce the confusion generally associated with explaining a problem or in any other technically related discussion.