Java is required for complete OpenOffice (OpenOffice.org) functionality. Java is mainly required for the HSQLDB database engine (used by our database product Base) and to make use of accessibility and assistive technologies. Furthermore some wizards rely on Java technology. See additional topics pertaining to the use of Java in OpenOffice.org and Apache OpenOffice in the Installation FAQ.
So what does this mean exactly? Base (the database component) relies completely on Java technologies to run, but other programs (like Writer, Calc and Impress) only need Java for special functionality. If you do not need to use Base and do not want to use any of the Wizards, then you do not need to have Java installed and configured for running Apache OpenOffice (and older versions of OpenOffice.org). You can completely prevent OpenOffice from prompting you about the use of Java by telling OpenOffice not to use a Java runtime environment (JRE). From the OpenOffice main menu use: "Tools - OpenOffice.org - Java", and uncheck "Use a Java runtime environment". However, we do recommend that you have a JRE on your system to take full advantage of OpenOffice's features without any issues.
Legacy versions of OpenOffice.org 3.3.0 and older included a JRE packaged with the download. Apache OpenOffice 3.4.0 and newer do not.
You will need to have a JRE version (32-bit or 64-bit) that is compatible with the architecture of the Apache OpenOffice version you downloaded. If you already have a JRE installed on your system that satisfies this requirement in one of the standard areas for Java installation, OpenOffice should detect this installation and let you choose it for use in OpenOffice via the "Tools - OpenOffice.org - Java". If you have a JRE installed that is not detected, you should be able to add it through this same menu. And, you can install a JRE or configure OpenOffice to use Java at any time to get missing functionality to work.
Important note for all Windows users:
The Windows version of OpenOffice is 32-bit. It installs and operates on both 32-bit and 64-bit versions of Microsoft Windows. However, a 32-bit Java Runtime Environment is required for any use of a JRE by 32-bit applications such as Apache OpenOffice. The 32-bit JRE must be in addition to any 64-bit JRE that is also installed.
The current versions of Apache OpenOffice work reliably with a variety of JREs including Oracle Java, versions 6 and 7 and openJDK, versions 6 and 7. Feel free to download a JRE from either of these sites if you feel you need this functionality.
Please report any problems you experience with using Java on OpenOffice through our bug reporting system, Bugzilla, or one of the other support venues listed in the Apache OpenOffice Support webpage, either the users list or forums.
For installing Java on Windows machines, one might appreciate: Download Instructions for Windows offline.