976140 ObjectOriented Programming

1

• 976-140 Object-Oriented Programming
• 344-202 Introduction to OOP
• ???????????????????

8. Inheritance
Faculty of Technology and
Environment
Prince of Songkla University, Phuket Campus


2/2551
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Why inheritance?

• How to programming for all characters in the game?

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Why inheritance?
GradStudent Id Name Major thesis register() checkG
rade() listConference()
Staff Id Name Office Salary paySalary() checkDayOf
f()
Lecturer Id Name Office Salary assignCourse() payS
alary() checkDayOff()
Student Id Name Major register() checkGrade() chec
kActivity()
Reuse
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Reuse

• OOP ?????????????????????????????????????????
  (reuse)
• ???? ?????????????????????????????????????????????
  ? ??? ????
• ????????????????????????????????????????
  ????????????????????????
• Reuse ????????
• ????????????? (Inheritance)
• ????????????? (Composition)

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"is a" versus "has a" Relationships

• ??????????????????????? 2 ??? ??????
• ??????????????? is a ?????????????
  (Inheritance)
• ??????????? subclass ?????????????
• a car is a vehicle
• ??????????????? has a ?????????????
  (Composition)
• ??????????????????????? attribute
• a car has wheels

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Composition

• ????????????? ????????????????????????????????????
  ??????
• Example
• public class Address
• String number
• String road
• String city
• String province
• String postcode
• public class Person
• String name
• String birthDate
• Address address

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Inheritance ?????????

• ????????? (Inheritance) ????????????????????????
  OOP ??????????????????????????????????????????????
  ????
• ???????????????????? ?????????????(attributes)????
  ?????????(behaviour) ???????????
• ????????????????????????????????? ????????
  ??????? (parent class / superclass / based
  class)
• ???????????????????????????? ????????
  ??????? (child class / subclass / derived class )

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Inheritance class diagram

• A ?????????????? B ??????? B ????????????????????
  A

A
???????
Vehicle
???????????????????????????
B
???????
Bicycle
Car
Helicopter
Racing
Sedan
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Inheritance

• ??????? ???????????????? ? ???? ? ?? (general)
• ??????? ??????????????????? ??????????????????????
  ????????? (specialize)
• ????????????????? ?????????????????????? Object
  ???????????????????
• Attribute ??? method ??????????????????
  ????????????????????? ???????????????
  ????????????????????
• ?????????????????? attribute ??? method ???????
• ???????????????????????????????????????????????

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Inheritance

• Redesign the Student classes with inheritance

Student Id Name Major register() checkGrade()
Student
GradStudent thesis listConference()
UnderGradStudent checkActivity()
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Keyword extends

• ????????????????????????????????????????????
  ???????????????????????????????????? extends
• Syntax
• modifier class ??????????? extends
  ???????????
• ????
• public class GradStudent extends Student
• public class Car extends Vehicle
• public class Manager extends Employee

Employee
Manager
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Ex. InherritanceDemo1
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Ex. InherritanceDemo1
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Keyword extends
Student
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Keyword extends

• ??????????????????????????????????????????????????
  ??
• ??????????????????????????????????????????????????
  ????????

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java.lang.Object

• ?????????? ?????????????????????????? Object
  ?????????? package java.lang
• ????????????????????????????????????????????????
  ??????????????????????? Object ?????????
• ????????????? extends ????????????????????????????
  ?????????
• ??????????????????????????????????????????????????
  ?

Object
Vehicle
Car
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The methods of the Object class

• Object ????????????????????? ??????????? Object
  ???????????????????
• ??????????? Object ???????? Java API
  (http//java.sun.com) ????
• public String toString() ?????? String ?????????
  object

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Ex.
Object
Radio
ToStringDemo
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Keyword null

• ???????????????? object ????????? null ?????
  object ????????????????????????????????????? ????
  object ????????????????? Garbage Collector
• Garbage Collector ?? JVM ?????????????? object
  ?????????????????????????? object
  ???????????????????

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Method overriding

• ??????????????????????????????????????????????????
  ???????????????? ???????? ????? method overriding
• Overridden method ??? ?????????????????????????
  override
• Overriding method ??? ??????????????????????
  override
• ?????????????????? ????????? ????????????????????
  ??????????????????????? ??????????????????

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Ex. Method overriding
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Ex. Method overriding
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Ex. Method overriding
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Keyword this

• this ????????? 2 ????
• ??????? 1 ????????????????????????? ??? object
  ??? this ???????????? reference
  ?????????????????????????????????????

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Keyword this

• ??????? 2 ??? this ????? constructor ???? ?
  ??????

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Keyword super

• ??? super ??? 2 ????
• ??????? 1 ??? super ?????????????????????????????

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Keyword super
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Keyword super

• ??????? 2 ???????? constructor
  ?????????????????? ??????????????????????????????
  constructor ????????????

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Find some errors
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Shadowing Data Fields

• ???? ?????????????????????????????????????????????
  ????
• ???????????????????????????????????????????
  ??????????????????????????????????????????
• ?????????????????????????????????????? ???????
  keyword super

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Shadowing Data Fields
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Shadowing Data Fields
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Keyword final

• Final class ??? class ??????????????? final
  ???????????????????????????

Compile error!!! InheritanceDemo1.java12 cannot
inherit from final Employee
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Keyword final

• Final method ?????????????? final
  ??????????????? override ??????

Compile error!!! InheritanceDemo1.java14
printData() in Manager cannot override
printData() in Employee overridden method is
final
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Access modifier

• Access modifier ???????????????????? ??????
  ???????? ?????????????????????????? ???????? 4
  ?????
• public ???????????????????????????????????
• protected ??????????????????????????????????
  package ????????????????????????????
• package ????????????? package ???????????????????
  ?????????????????
• private ????????????????????? private
  ?????????????????????????????????????????

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Access modifier

• ????????? access modifier
• class
  attribute method
• public / / /
• protected X / /
• package / / /
• private X / /
• ???????????????????? package ????????????????
  ?????? ?????????????????????? access modifier
  ???

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Inheriting attributes and methods

• ????????????????? ?????????????? ??????? private
  ???????????????????????????

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Inheriting attributes and methods
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Inheriting attributes and methods

• ???????????????????? attributed ??? method
  ??????????????????????? protected ??? ???????
  package???
• ?????????????????????? package ?????????????
  package ????????????????
• package a
  package b

A
B
C
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Inheriting attributes and methods
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Inheritance and constructor

• ???????? object ??????????????????? default
  constructor ????????? ?????????????????????????
  constructor ?????????????

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Summary

• ??? reuse class ????? 2 ?????? inheritance
  composition
• ????????????????????????????????????????????????
• ??????????????????? attribute ??? method ???????
  public, protected ???
• ?????????? private ??????
• Method overriding ????????????????????????????????
  ?????
• this ??????????????????????????????????
• super ?????????????????????????????????
• Class ??????? final ??????????????????
• Method ??????? final ????????? overrided ???
• Constructor ???????????????????????????