Inheritance cont.

1
Inheritance cont.

• Abstract classes
• Abstract methods
• Example
• Abstract class - Shape
• Derived concrete classes - Circle, Rect
• Prepare for the Exam.

2
Abstract classes

• Abstract classes are classes without instances.
• For abstract class Animal
• pubic abstract class Animal
• public virtual void Eat()
• We can not create Animal objects
• Animal error new Animal()
• An abstract class is often derived by concrete
  classes.
• public class Cat Animal
• public class Dog Animal
• .
• Example file Example58

3
Abstract classes

• A base class can be declared as a abstract class
  it has no real instances.
• For instance, we can declare BankAccount as an
  abstract class.
• So abstract classes are also used to specify
  common data and operations to derived concrete
  derived classes.

4
Abstract methods

• Moreover, we can declare abstract methods in an
  abstract class.
• public abstract void Eat()
• Abstract methods has no body in the abstract
  class
• Abstract methods must be implemented in derived
  class with keyword override.
• Compare to virtual methods
• An virtual method must have a body.
• Derived may or may not override a virtual methods
• Example Animal
• Example58 - public abstract string Speak()

5
Programming exercise

• Given class Point
• public class Point
• private double x
• private double y
• public Point(double x, double y)
• this.x x
• this.y y
• public double X
• get return x
• public double Y

• Define abstract class Shape
• An instance variable
• private Point location
• An abstract method
• public abstract double Area()
• Define 2 derived concrete classes Rect and Circle
• Rect
• One more instance variable
• private Point toPoint
• Circle
• One more instance variable
• private double radius

6
Exam 3 (4/15, Fri)

• Topics covered since exam 2
• The String class and string operations (chapter
  6.16.2)
• ToUpper, ToLower, IndexOf, Replace, SubString,
  CompareTo
• The Random class and random number generation
  (chapter 6.5)
• Next, NextDouble
• Interfaces and implementation (chapter 6.4)
• Implement interface IComparable , CompareTo
  method , sorting an array
• Two dimensional array (chapter 7.4)
• Inheritance base classes, derived classes,
  abstract classes. (chapter 10)