Can one class extend two classes?

Java doesn't support multiple inheritance. You can implement multiple interfaces, but not extend multiple classes.

Java does not support multiple inheritance.

There are a few workarounds I can think of:

The first is aggregation: make a class that takes those two activities as fields.

The second is to use interfaces.

The third is to rethink your design: does it make sense for a Preferences class to be both a PreferenceActivity and an AbstractBillingActivity?