To the best of my knowledge, Java abstract classes cannot generally be used in Matlab, since you cannot instantiate an object of an abstract class (duh!). If the abstract class has some static methods or fields, then you can use them, but this is not the case in general.
To extend such classes, create a new Java class that extends them, and this can then be used within Matlab.
To explore the contents of Java classes (including abstract classes) in Matlab, you can use my UIINSPECT and CheckClass utilities on the Matlab File Exchange (they accept a class name as input arg).
