There are two principal products in the JavaTM 2 Platform, Standard Edition,
(J2SETM) platform family.
Java Runtime Environment (RE)
The Java RE provides the
libraries, Java virtual machine, and other components necessary
for you to run applets and applications written in the Java
programming language. It does not contain
tools and utilities such as compilers or debuggers for developing
applets and applications.
Java 2 Software Development Kit (SDK)
The Java 2 SDK is a superset of the Java RE.
The Java 2 SDK contains everything that's in the Java RE,
plus additional tools such as compilers and debuggers that are
necessary for developing applets and applications.
Question: Why would anyone want the Java RE if the
Java 2 SDK has everything in the Java RE and more?
Answer: The Java RE is smaller and therefore easier to
download or distribute with software than the Java 2 SDK. Most users
of Java technology are people
who just want to run applets and applications developed by others.
They're not interested in developing any applications themselves.
The relatively small Java RE is made for such
end users. They can download the Java RE themselves
from the web, or software vendors can include it in their own
products. The typical end-user doesn't need the bulkier Java 2 SDK
with its development tools.
-- Download page from which you can obtain version 1.4.2 of both the
Java 2 SDK and the JRE.
J2SE 1.4.2 Platform Documentation -- Table of contents for the J2SE 1.4.2 platform
documentation, with links to API specifications, user guides, tool
documentation, and more.