Java tidbidz 2: Abstract class and Interface

• Interface variables static and final by default [interfaces cannot be instantiated in their own right; the value of the variable must be assigned in a static context in which no instance exists. The final modifier ensures the value assigned to the interface variable is a true constant that cannot be re-assigned by program code.]

• We can have abstract class without abstract method but not abstract method in non-abstract class, because declaring a class abstract only means that you don't allow it to be instantiated on its own, while an abstract method must be defined by subclasses.

• You can even have abstract classes with final methods but never final classes with abstract methods.