Polymorphism

• Automatic in Java, not true for C++ where programmer must include virtual keyword
• When a base class reference invokes a method
• The true type of the object being referred to is determined
• If the true type does not have a matching method, the base class method is executed
• If the base class doesn't have the method's interface, the program would not have compiled
• Can't call a method that is specific to a subclass via a base class reference
• If the true type oof the object is, in fact, a base class type, it will simple execute the base class method

Abstract Methods and Classes

• Force all subclasses to provide an implementation, specify the method is abstract in the base class
• Subclasses that don't implement the abstract method can not be compile
• Abstract methods don't have n implementation at he base class, since all subclasses are required to implement it, there is no need for a method body at the base class level
• A class that contains some abstract functions in an abstract class. In java, programmer must specify a class is abstract
• Cannot create objects of an abstract type

Final Methods and Classes

• Saying a method is final means the method cannot be overriden by a subclass
• Saying a class is final means the class may not be extended

Why do this?

• It's faster, compiler doesn't have to look up the method call tree