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Inheritance, part 4 Abstract classes/methods

Inheritance, part 4 Abstract classes/methods. COMP 401, Spring 2013 Lecture 12 2/19/2013. Midterm Curve. Average: 67.55 Std Dev : 14.45. The next few weeks. Th 2/21 Assignment 4 will be released (due M 3/4, syllabus says 3/1) Composition and Delegation Tu 2/26, Th 2/28 kmp in Olso

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Inheritance, part 4 Abstract classes/methods

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  1. Inheritance, part 4Abstract classes/methods COMP 401, Spring 2013 Lecture 12 2/19/2013

  2. Midterm Curve • Average: 67.55 • StdDev: 14.45

  3. The next few weeks • Th 2/21 • Assignment 4 will be released (due M 3/4, syllabus says 3/1) • Composition and Delegation • Tu2/26, Th 2/28 • kmp in Olso • Two lectures on exceptions by Prof. Dewan • Tu 3/5 • kmp goes to Washington • Pre-recorded lecture on Factory Pattern • A5 Released (due 3/18) • Th 3/7 • Cancelled • Tu3/12, Th 3/14 • Spring Break

  4. Inheritance Recap • Subinterfacing • Adding methods to create a new “contract” • Subclassing • Inherits fields and methods from parent class • Visibility controlled by access modifier • Adds subclass specific fields and methods • Constructor relationship • Overloading parent methods • Subclass methods with different signatures • Overriding parent methods • Subclass methods with same signature • Always virtual • super keyword provides a mechanism to call parent class version of a method

  5. Using inheritance • Example starts with several related classes that are implemented independently. • BlackBear • PolarBear • Python • Robin

  6. Common behavior • Refactor common behaviors into a common parent interface. • Animal interface

  7. Common object state • Refactor common object fields into a common parent class • AnimalImpl

  8. Common implementation • Refactor common method implementations into parent class. • Use overriding if subclasses need to do something special or different. • AnimalImpl

  9. Common behavior with uncommon implementation • Notice speak() is a common behavior. • So we want it to be part of Animal interface • But no common implementation. • Each subclass of animal will have a different way of speaking. • No good default or commonalities in way of speaking that can be specified at parent class.

  10. Abstract Classes and Methods • Parent class has no meaningful implementation of a method. • But part of interface of parent class • Expect subclass to provide it. • In these situations, we never expect (or want) the parent class to be instantiated directly. • We always make new objects using a subclass. • Syntax • Use “abstract” modifier when declaring parent class • Declare any methods that must be provided by subclass in parent • Add “abstract” modifier to method signature. • Follow signature with semicolon instead of method definition

  11. Example Revisited • AnimalImpl

  12. Repeat Exercise with Bears

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