The new and update clauses of installjava indicate whether you want new classes to replace currently installed classes.
If you specify new, you cannot install a class with the same name as an existing class.
If you specify update, you can install a class with the same name as an existing class, and the newly installed class replaces the existing class.
WARNING! If you alter a class used as a column datatype by reinstalling a modified version of the class, make sure that the modified class can read and use existing objects (rows) in tables using that class as a datatype. Otherwise, you may be unable to access existing objects without reinstalling the original class.
Substitution of new classes for installed classes depends also on whether the classes being installed or the already installed classes are associated with a JAR. Thus:
If you update a JAR, all classes in the existing JAR are deleted and replaced with classes in the new JAR.
A class can be associated only with a single JAR. You cannot install a class in one JAR if a class of that same name is already installed and associated with another JAR. Similarly, you cannot install a class not-associated with a JAR if that class is currently installed and associated with a JAR.
You can, however, install a class in a retained JAR with the same name as an installed class not associated with a JAR. In this case, the class not associated with a JAR is deleted and the new class of the same name is associated with the new JAR.
If you want to reorganize your installed classes in new JARs, you may find it easier to first disassociate the affected classes from their JARs. See “Retaining classes” for more information.