COMP 121

1
COMP 121

• Week 03

2
Agenda

• Review this weeks expected outcomes
• Review Guided Learning Activity solutions
• Introduce homework problems
• Question and answer session

3
Outcomes

• Explain the purpose, uses, and scope of inner
  classes.
• Describe inheritance and the Java mechanisms that
  implement it.
• Distinguish between overloaded and overridden
  methods.
• Organize a set of related classes into an
  inheritance hierarchy.
• Determine when and how to call superclass methods
  from within a subclass.
• Apply the rules of implicit and explicit object
  conversion.

4
Inner Classes

• Defined at same level as members and methods
• Are associated with a parent object of the
  outer class type
• Can access members of the parent object

5
Inner Classes

• public class ProgramGuide
• private Listing listings
• private interface ListingComparator
• int compare(Listing first, Listing second)
• private class ChannelListingComparator
• implements ListingComparator
• public int compare(Listing first, Listing
  second)
• // code
• // NameListingComparator here, too.

6

• Guided Learning
• Activity Solutions for Week 03

7
Learning Activities

• Activity 3-1
• Outcome Explain the purpose, uses, and scope of
  inner classes.

8
Inheritance

• Derivation - The process of defining a new class
  based on an existing class.
• Base Class - The existing class that is used to
  define the new class.
• Derived Class - The new class defined using the
  base class.
• Inheritance - The inclusion of members and
  methods from a base class in a derived class.
• A base class and a derived class should have an
  is a relationship.

9
Inheritance

• class Animal public void eat()
• class Dog extends Animal public void bark()
  
• class Retriever extends Dog public void
  retrieve()
• class Collie extends Dog public void
  saveTimmy()
•  
• Animal is the base class for Dog.
• Dog is derived from Animal.
• Retriever is derived from Dog.
• Dog is the base class for Retriever.
• Dog and Animal are superclasses of Retriever and
  Collie.
• Dog, Collie, and Retriever are subclasses of
  Animal.

10
Inheritance

• public class Animal
• private String type
•  
• public Animal(String t) type t
•  
• public String toString()
• return This is a type
•  

11
Inheritance

• class Animal
• void toString() return This is a type
•  
• class Dog extends Animal
• void toString()
• return super.toString() \nIts
• name the breed
•  
• public static void main(String args)
• Dog d new Dog(Rex, German Shepherd)
• Dog d2 new Dog(Lassie, Collie)
• System.out.println(d d2)

12
Learning Activities

• Activity 3-2
• Outcome Describe inheritance and the Java
  mechanisms that implement it.
• Activity 3-3
• Outcome Distinguish between overloaded and
  overridden methods.

13
Learning Activities

• public class A
• void method1()
• void method3(String s)
•  
• public class B extends A
• void method1(int x) / Overload
  parameters are different /
• void method3(String s) / Overrides
  A.method3 /
•  
• public class C extends A
• void method1() / Overrides A.method1 /
• void method2(int x, int y) / New method /
  
• void method2(int y, char c) / Overloads
  method2 /

14
Learning Activities

• public class D
• void method3()
• void method1()
• void method2(int y, char c)
• public class C
• void method1()
• void method2(int x, int y)
• void method2(int y, char c)
• public class B extends C
• void method1(int x) / Overloads method1 /
  
• void method3(String s) / New method /
• public class A extends B
• void method1() / Overrides C.method1 /

15
Learning Activities

• Activity 3-4
• Outcome Organize a set of related classes into
  an inheritance hierarchy.

16
Learning Activities

• public class Publication
• private String isbn
• private int state // writing, editing,
  preproduction, done
• private Date writingDeadline
• private Date editingDeadline
• private Date preproductionDeadline
• private Date publicationDeadline
• public String getISBN() return isbn
• public void setISBN(String isbn) this.isbn
  isbn
• // More get/set methods

17
Learning Activities

• public class Book extends Publication
• private boolean isPaperback
• private String author
• private double royaltiesPaid
• // get/set methods for isPaperback, author, and
  royaltiesPaid
• public class Magazine extends Publication
• private String editor
• // get/setEditor
• public class Pamphlet extends Publication
• // Nothing here

18
Inheritance

• public class Dog extends Animal
• private String name
• private String breed
•  
• // Will this work?
• public Dog(String n, String b)
• name n
• breed b
•  
• public Dog(String n, String b)
• super(Dog)
• name n
• breed b
•  

19
Inheritance

• class Animal
• void display() System.out.println(This is a
  type)
•  
• class Dog extends Animal
• void display()
• super.display()
• System.out.println(\nIts name the
  breed)
•  
• public static void main(String args)
• Dog d new Dog(Rex, German Shepherd)
• Dog d2 new Dog(Lassie, Collie)
• d.display()
• d2.display()

20
Inheritance and Casting

• class Dog
• class Husky extends Dog
• Dog d new Husky() // Legal implicit cast
• Husky h d // Illegal needs explicit cast
• Husky h (Husky)d // Legal
• Husky h (Husky)new Dog() // Throws exception

21
Learning Activities

• Activity 3-5
• Outcome Determine when and how to call
  superclass methods from within a subclass.
• Activity 3-6
• Outcome Apply the rules of implicit and
  explicit object conversion.

22
Learning Activities

• Polygon is the superclass, Triangle is the
  subclass
• Polygon p new Triangle()
• Triangle t (Triangle)p // cast required
• Triangle t (Triangle)new Polygon() //
  ClassCastException
• GraduateStudent is the subclass, Student is the
  superclass
• Student s new GraduateStudent()
• GraduateStudent gs (GraduateStudent)s // cast
  required
• Person is the superclass, Student is the subclass
• Person p new Student()
• Student s (Student)p

23
Learning Activities

• Vehicle is the superclass, Car is the subclass
• Vehicle v new Car()
• Car c (Car)v // cast required
• Vehicle is the superclass, Minivan is the
  subclass
• Vehicle v new Minivan()
• Minivan m (Minivan)v // cast required
• Vehicle is the superclass, Truck is the subclass
• Vehicle v new Truck()
• Truck t (Truck)v // cast required

24
Homework Assignments

• Due this week
• Homework 1
• Due next week
• Lab 1
• Homework 2
• Draft Reflection Paper

25

• Question and Answer Session