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#### 10.2.1 Class Path

The classpath is the list of places that Java looks to find the bits of compiled code that it uses to run an application. When running TOPCAT this always has to include the TOPCAT classes themselves - this is part of the usual invocation and is described in Section 10. However, for certain things Java might need to find some other classes, in particular for:

- JDBC drivers (see Section 10.3)
- Providing extended algebraic functions (see Section 7.11)
- Installing I/O handlers for new table formats (see Section 4.1.4)

If you are going to use these facilities you will need to start the program with additional class path elements that point to the location of the classes required. How you do this depends on how you are invoking TOPCAT. If you are using tht `topcat` startup script, you can write:

        topcat -classpath other-paths ...

(this adds the given paths to the standard ones required for TOPCAT itself). If you are invoking java directly, then you can either write on the command line:

        java -classpath path/to/topcat.jar:other-paths
             uk.ac.starlink.topcat.Driver ...

or set the CLASSPATH environment variable something like this:

        setenv CLASSPATH path/to/topcat.jar:other-paths

In any case, multiple (extra) paths should be separated by colons in the other-paths string.

Note that if you are running TOPCAT using java's `-jar` flag, any attempt you make to specify the classpath will be ignored! This is to do with Java's security model. If you need to specify a classpath which includes more than the TOPCAT classes themselves, you can't use `java -jar` (use `java -classpath topcat-full.jar:... uk.ac.starlink.topcat.Driver` instead).

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk