Knowledge Base

Notice Information in this article applies to Excelsior JET versions 3.0 through 3.7.


You have a copy of the Java Runtime Environment (JRE) installed in a certain directory on your system, but JET Setup does not display it in the list of JREs found. Selecting that directory manually results in an error message saying that the selected directory does not contain a supported version of the JRE.


To understand why JET Setup may reject the manually specified JRE location, consider the following.

  1. Excelsior JET is designed to work in conjunction with the Sun JRE. It will not work with e.g. IBM JRE.
  2. Excelsior JET does not support Sun JRE betas and release candidates.
  3. Sun JRE versions have format 1.X.Y_ZZ (e.g. 1.3.1_02), where ZZ is the microversion. The JET Setup utility uses some build and fine tuning information specific to particular JRE microversions. So a given version of Excelsior JET is only tested against final releases of each JRE microversion available at the beginning of the QA phase for that version of Excelsior JET.

    As a result, for JRE (micro)versions that were released after, or shortly before the release date of the version of Excelsior JET that you are using, chances are high that your copy of Excelsior JET does not support them. For instance, Excelsior JET 3.11 supports Java 2 microversions up to and including 1.3.0_05, 1.3.1_07, 1.4.0_04 and 1.4.1_02. It will not work with JRE 1.4.2 (but the next version will.)

    To check the version number of the given JRE installation, run

        JRE-directory\bin\java -version

    The first line of output will say

        java version "version"

  4. Some products, such as IntelliJ IDEA or older versions of Borland JBuilder, come with a slightly modified JRE, and there are also products that can modify a JRE installed in a public location, such as C:\Program Files\Javasoft\. Such modification may prevent succesful compilation of Java 2 platform classes, compromise application performance and cause subtle problems at application compile and run time, so JET Setup checks the selected JRE directory for consistency. If its contents do not match contents of an original Sun’s JRE package, the directory will be rejected.
  5. Excelsior JET, Personal Edition may only work with a non-redistributable JRE, which is installed as part of the respective JDK, so JET Setup in the Personal Edition will not allow you to select a redistributable JRE.

This behavior is by design.


Install one of the JRE versions that are supported by your copy of Excelsior JET, making sure you are installing the original package made by Sun Microsystems.

If you want to use a JRE microversion that is newer than your copy of Excelsior JET, check if there is an update available for download.

If your JRE version is far beyond the range of versions supported by your copy of Excelsior JET, you may need to upgrade to a newer version of Excelsior JET.


  1. Article 000006
  2. Archived Java 2 releases at

Article ID: 7
Last Revised On: 26-Sep-2003