[PDF] EECS2030: Advanced Object Oriented Programming Section F

Can class methods in an abstract class be abstract?

Class methods in an abstract class cannot be abstract. Ø The heading public interface X means X cannot contain anything but non - final instance method headings (with a semicolon in place of the body) and final class variables. A non -abstract object class with the heading class Y implements X must define all methods in that interface .

Does Boolean have a comparable interface?

Boolean does not implement the Comparable interface, but it does have instance methods equals and toString that override the corresponding methods in the Object class. The only constructor for the Character class has a char parameter, as in new Character ('B') .

What is the difference between an interface and a superclass?

An interface has only method headings, with no method bodies allowed. So you need something in between an interface (where all methods must be overridden ) and a "concrete" superclass (all methods defined, so overriding is always optional). The recommended Java solution in this case is an abstract class .

How does a non-abstract object class implement X?

A non -abstract object class with the heading class Y implements X must define all methods in that interface . A class may implement many interfaces (use implement X,U,Z ) but may subclass only one class. Ø The compiler binds a method call t o a particular method definition when it can, namely, for a class method or for a final instance method.