Bobby D. Gerardo

1
Programming and Problem Solving Using Java

• Bobby D. Gerardo
• Kunsan National University
• Summer 2004

2
Chapter 6Class Hierarchies, Inheritance, and
Interfaces
3
Review
4
(No Transcript)
5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
Sorting an Array

• Method
• IntArray.selectionSort(scores)

14
(No Transcript)
15
Array Search

• Search method
• i.e. int index IntArray.search(scores, 100)

16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
Chapter 6Class Hierarchies, Inheritance, and
Interfaces
20
Class Hierarchies, Inheritance, and Interfaces

• Throughout the book we followed object oriented
  design techniques by using abstraction modeling
  real life entities by retaining only essential
  information.
• We also use encapsulation clustering data and
  methods together into classes, providing safe and
  reliable boundaries.
• This chapter enhances our capability to use
  object oriented design by introducing key
  features such as hierarchies, inheritance, and
  interfaces.

21
Class Hierarchies and Inheritance

• Code reuse is very important concept in OOP
• If you build new applications using code that has
  been written and tested, you are more likely to
  develop programs are error free.
• Extending the existing class
• Subclass with additional data field
• Objects also inherit the data fields and methods
  of the original class called superclass.

22
Class Hierarchies and Inheritance (cont)

• Hierarchies and inheritance is a rich concept
  that often appear in science
• Inheritance, in combination with hierarchical
  organizations, allows you to capture the idea
  that one thing maybe a refinement or extension of
  another.

23
is a versus has a Relationships

• Java allows you to capture both the inheritance
  (is a) relationship and the has a relationship.
  For example, a car class might be declared as
  follows
• public class Car extends Vehicle
• Wheels w new Wheels4 //cars have 4
  wheels
• The keyword extends specifies that Car is a
  subclass of Vehicle.

24
Case Study 1 A Hierarchy of Employee Classes
25
Case Study 1 A hierarchy of Employee Classes

• Problem You have a class called NewEmployee
  that stores basic data about an employee name,
  social security number, job title, address, phone
  number, age, starting year of employment, and
  total pay to date. Besides accessor and modifier
  methods, this class has a method to compute the
  employees numbers of years with the company, one
  to compute the number of years to retirement, and
  one to update the total pay to date. It also has
  a toString() method.

26
Case Study 1 A hierarchy of Employee Classes
(cont)

• Now suppose you decide to differentiate between
  two kinds of employees salaried and hourly
  employees. Hourly employees are paid an hourly
  rate and their weekly pay varies depending on how
  many hours they work. Salaried employees, on the
  other hand, have a fixed annual salary and their
  weekly pay rate is the same regardless of how
  many hours of work.

27
Analysis and Design

• Fig. 6.2 shows a description of class
  NewEmployee. In addition to the methods described
  above, we added an equals() method that compares
  two NewEmployee objects.

Fig. 6.2 Class NewEmployee
Data Fields Attributes String
name Name String socSecNum Social security
number String jobTitle Job Title String
address Address String phoneNumber Phone
Number int age Age int startYear Starting
year of employment double totalPay Total pay to
date Methods Behavior . .
28
Implementation

• Fig. 6.5 shows the NewEmployee class. The
  declaration statements for the type String data
  fields initialize them to empty string ( ). The
  numeric data fields are initialized to zero (the
  default value).
• See Fig. 6.5 in the book.

29
Testing

• Fig. 6.9 (in the book) shows a class that tests
  all three employees classes.
• Fig. 6.10 (in the book) shows the console window
  after the class executes.

30
Operations in Class Hierarchy

• Fig. 6.11 shows the class hierarchy for the
  employee classes developed in the last section.

Fig. 6.11 Class hierarchy
31
Operations in Class Hierarchy (2)

• Fig. 6.12 Data fields and methods for class
  NewEmployee
• Fig. 6.13 Data fields and methods for class
  SalaryEmployee
• Fig. 6.14 Data fields and methods for class
  NewEmployeeHourly

32
Operations in Class Hierarchy (3)

• Method overloading When class has multiple
  methods with the same name.
• A method signature consists of the method name
  and its parameter lists
• Method overriding The fact that a method
  defined in a subclass blocks the execution of a
  method with the same signature defined in its
  superclass is called method overriding.

33
Operations in Class Hierarchy (4)

• Protected visibility
• Shadowing data fields
• Misnomer of Superclass and Subclass
• Assignment in a Class Hierarchy
• Casting in a Class Hierarchy
• Passing Objects as Arguments

34
Polymorphism

• We will study how we can store objects of
  different types in a single array and process
  them in a uniform way using a programming
  language feature called polymorphism.

35
Polymorphism and Late Binding of Method Calls

• The feature that enables a particular method call
  to have behavior at different times is called
  polymorphism, which means multiple forms.
• The feature that enables a programming language
  to select a code fragment to execute at run-time
  is called dynamic binding.

36
Case Study 2 A Company with an Array of
Employees of Different Types
37
Case Study 2 A Company with an Array of
Employees of Different Types

• Problem In section 5.5, we showed how to
  process an array of employees in which each
  element was the same type (Employees). Now our
  company has several employees of different types
  (NewEmployee, HourlyEmployee, SalaryEmployee). We
  want to store them in an array and compute the
  total company payroll.

38
Interfaces

• An interface is used to specify a set of
  requirements that is imposed on a collection of
  classes.
• Classes that implement an interface are
  guaranteed to have certain functionality
  (behavior) and also inherit any constants that
  are defined in the interface.
• Form public interface InterfaceName
• abstract method headings
• constant declaration

39
Declaring Constants

• We can declare constants in an interface. These
  constants would be inherited by classes that
  implement the interface.
• public static final double DEDUCT_PCT 5.5
• In a class Payable to declare DEDUCT_PCT as a
  constant with a value of 5.5

40
The Comparable Interface and Method compareTo

• We can declare constants in an interface. One of
  these is the Comparable interface, ensures that
  the programmer will be able to compare objects in
  each class that implements it.
• All classes that implement the Comparable
  interface must have a compareTo method
• See Fig. 6.22 and Table 6.1

41
Abstract Classes

• Sometimes we need to new create class, called
  abstract class that should be instantiated and
  whose sole purpose is to serve as the parent
  (superclass) of a group of classes.
• Form public abstract class ClassName
• data field declaration
• abstract method headings
• method definitions

42
Case Study 3 Areas of Geometric Figures
43
Case Study 3 Areas of Geometric Figures

• Problem Consider the problem of finding the
  total area of a collection of geometric figures.
  This problem has many practical applications. For
  example in calculating the paint needed for a
  house, a painter might visualize the interior
  walls as a series of rectangular and triangular
  shapes. In calculating the amount of fertilizer
  to buy, a landscaper might represent a garden as
  a collection of circle and triangular shapes.

44
Case Study 4 Drawing of Geometric Figures
45
Case Study 4 Drawing of Geometric Figures

• Problem We would like to draw geometric figures
  on the screen. Each figure object will be one of
  our standard shapes and can appear anywhere on
  the screen with any interior color or border
  color.

46
Programming Projects

• Prog. Project 1, P. 436
• Prog. Project 2, P. 436
• Prog. Project 3, P. 436
• Prog. Project 4, P. 436

47
? End of Chapter