Can only have final static variables ... Only functional interfaces can use the lambda feature in Java. Abstract classes with only one abstract method cannot use lambdas. Can’t have constructor.

and final, and all interface methods are inherently public. The Java Tutorial goes on to list bullets for when an abstract class should be considered and for when an interface should be considered.

Java does enable the option to mark a class as final to eliminate the ability to perform inheritance complete, but that is often too heavy of a hammer to drop. Marking a class as final prevents all ...