chapter 8 a second look at classes and objects. section 8.1 static class members roomareas.java (...

Chapter 8 A Second Look at Classes and Objects

SECTION 8.1 STATIC CLASS MEMBERS

RoomAreas.java( 課本 p. 372)

Rectangle.java( 課本 p. 366)

main

Rectangle kitchen = new Rectangle (); // line 17

物件區

numbertotalArea

inputkitchen

bedroomden

length

width

main

Rectangle bedroom = new Rectangle ();// line 18

物件區

length

widthnumber

totalAreainput

kitchenbedroom

den

length

width

main

Rectangle den = new Rectangle (); // line 19

物件區

length

widthnumber

totalAreainput

kitchenbedroom

den

length

width

length

width

main

kitchen.setWidth(number); // line 29

物件區

10.0length

14.0width14.0number

totalAreainput

kitchenbedroom

den

length

width

length

width

Double

parseDoubl

e

“14”

setWidth

14.0

每個物件有自己的欄位方法只作用在「某個物件」的欄位

main

bedroom.setLength(number); // line 35

物件區

10.0length

14.0width14.0number

totalAreainput

kitchenbedroom

den

15.0length

width

length

width

Double

parseDoubl

e

“14”

15.0

setLength

每個物件有自己的欄位方法只作用在「某個物件」的欄位

main

totalArea = kitchen.getArea() + bedroom.getArea() + den.getArea();// line 52-53

物件區

10.0length

14.0width30.0number

totalAreainput

kitchenbedroom

den

15.0length

12.0width

20.0length

30.0width

“30”

getArea140.0

getArea

getArea

180.0

600.0

main

totalArea = kitchen.getArea() + bedroom.getArea() + den.getArea();// line 52-53

物件區

10.0length

14.0width30.0number

920.0totalAreainput

kitchenbedroom

den

15.0length

12.0width

20.0length

30.0width

“30”

getArea140.0

getArea

getArea

180.0

600.0+

+

問題討論• 新題目

– 條件 1: 程式必須印出長方形的個數– 條件 2: 由 Rectangle.java 提供計數功能

• Open – Labs\RoomAreas.java– Labs\RectangleOld.java

• Alice’s 解決方法 – // Alice: in RoomAreas.java– 符合條件 1

• Bob’s 解決方法 – // Bob: in two java files– 符合條件 1 & 2?

Non-static vs. Static

• Why Bob fails?– See ppt. 12– 物件欄位：每個物件均有一份欄位

• 物件方法兩特點 ( 課本 p. 522)– Compile Lab8_0.java– Compile Lab8_0_1.java– Ex: length() in String class; getAge() in Dog class

• Bob 應該使用 static– 修改程式– See ppt. 13-17

main

Bob 的方法 物件區

10.0length

width

setLength

numbertotalArea

inputkitchen

bedroomden

1count

15.0length

width1count

20.0length

width1count

setLength

setLength

getCount

1

main

正確的方法— static 的使用static private int count; 物件區

numbertotalArea

inputkitchen

bedroomden

0count

length

width

length

width

length

width

屬於整個 Rectangle類別

main

正確的方法— static 的使用 kitchen.setLength(number); 物件區

numbertotalArea

inputkitchen

bedroomden

1count

length

width

length

width

10.0length

width

main

正確的方法— static 的使用bedroom.setLength(number); 物件區

numbertotalArea

inputkitchen

bedroomden

2count

length

width

15.0length

width

10.0length

width

main

正確的方法— static 的使用den.setLength(number); 物件區

numbertotalArea

inputkitchen

bedroomden

3count

20.0length

width

15.0length

width

10.0length

width

main

正確的設計— static 的使用kitchen.getCount() 物件區

numbertotalArea

inputkitchen

bedroomden

3count

20.0length

width

15.0length

width

10.0length

widthgetCount

3

Static

• 靜態欄位特性 (p. 522)– Run Lab8_1.java

• 靜態欄位特性 (p. 522)– Run Lab8_1_1.java

• Run Countable.java (p. 522) & StaticDemo.java (p. 523)

– 修改 StaticDemo.java (#19)• object1 object3 • object1 Countable

Static Method

• 靜態方法：加上 static– Countable.java

• getInstanceCount 改為靜態方法– StaticDemo.java: 修改 #19

• 用途– 工具型類別提供服務

• Run Metric.java (p. 525) &MetricDemo.java (p. 526)

• See ppt. 20-4

– 操作靜態欄位• RectangleOld.java: static getCount()

2count

10.0length

width

• 靜態方法限制– Compile Lab8_2.java, Lab8_2_1.java, Lab8_2_2.java, Lab8_2_3.java

10.0length

width

Rectangle 類別

METRIC.JAVA & METRICDEMO.JAVA( 課本 pp. 567-8)

main

Line 17 (MetricDemo.java, p. 526)

DecimalFormat fmt = new DecimalFormat("0.00");

物件區

inputmileskilosfmt

ShowMessageDialog

ShowInputDialog

JOptionPane class

mToKkToM

Metric class

Double class

DecimalFormatclass

“0.00”

DecimalFormat

format

parseDoub

le

main

Line 21 (MetricDemo.java) 物件區

inputmileskilosfmt

ShowMessageDial

og

ShowInputDialog

JOptionPane class

mToKkToM

Metric class

Double class

DecimalFormatclass

“0.00”

DecimalFormat format

“10”

parseDoubl

e

main

Line 23 (MetricDemo.java)

miles = Double.parseDouble(input); 物件區

input10.0miles

kilosfmt

ShowMessageDial

og

ShowInputDialog

JOptionPane class

mToKkToM

Metric class

Double class

DecimalFormatclass

“0.00”

DecimalFormat format

“10”

parseDoubl

e

main

Line 26 (MetricDemo.java)

kilos = Metric.milesToKilometers(miles); 物件區

input10.0miles

16.09kilosfmt

ShowMessageDial

og

ShowInputDialog

JOptionPane class

mToKkToM

Metric class

Double class

DecimalFormatclass

“0.00”

DecimalFormat format

“10”

parseDoubl

e

10.0

Static 效果

2count

10.0length

4weight

10.0length

2weightamanda

• In main– Dog.length // 哪個 ? – amanda.length // – Dog.count // – amanda.count //

bob

Dog

main

Static 效果

2count

10.0length

4weight

10.0length

2weightamanda

• In M1– length • 執行哪個 M1 ，就用哪

個 length

– count • 就是靜態欄位 count• 只有一個

bob

Dog

M1

M1

Static 效果

2count

10.0length

4weight

10.0length

2weightamanda

• In M2– length • 用哪個 length?

– count • 就是靜態欄位 count• 只有一個 bob

Dog

M2

SECTION 8.4 THE TOSTRING METHOD

(p. 533)

toString

• Run Lab8_3.java• String toString()– 回傳物件狀態的標準方法– UML: See Figure 8-8 (p. 534)

– 執行時機 ( 課本 p. 536)

• Run Stock Class Phase 1 \Stock.java (p. 535) & StockDemo1.java (p. 537)

• 課堂實作– 請將 Lab8_3.java 中的 Dog 類別增添 toString 功能– 請用「狗狗姓名 + “@” + 狗狗年齡」代表物件字串

SECTION 8.5 WRITING AN EQUALS METHOD

(p. 537)

比較物件• Run Labs\BadStockCompare.java & Stock.java• 利用 == 運算子比較– See ppt. 32-4– 比較物件的記憶體位置

• 比較物件的欄位內容• boolean equals(Stock o)– Run Stock Class Phase 2\StockCompare.java(p. 539)

– See ppt. 36-8– 比較邏輯 ( 課本 p. ?)

main

Stock company1 = new Stock("XYZ", 9.62); // line 12

物件區

company1company2

symbol

5

9.62sharePrice

“XYZ”

main

Stock company2 = new Stock("XYZ", 9.62); // line 13

物件區

company1company2

symbol

5

9.62sharePrice

“XYZ”

symbol

5

9.62sharePrice

“XYZ”

main

if (company1 == company2) // line 17

物件區

company1company2

symbol

5

9.62sharePrice

“XYZ”

symbol

5

9.62sharePrice

“XYZ”

STOCKCOMPARE.JAVA(p. 539)

main

if (company1.equals(company2)) // line 15

物件區

company1company2

symbol

4

9.62sharePrice

“XYZ”

symbol

5

9.62sharePrice

“XYZ”

equals

主程式之所以知道要呼叫company1.equals(company2) ，是因為：(1)company1 與 company2 都屬於 Stock 類別(2)Stock 類別提供了 equals 方法可供比較

類別設計者為何寫 equals(Stock object2) ：(3) 提供比較服務(4) 傳入另一物件與方法所啟動的物件做比較

main

if (symbol.equals(object2.symbol) && // line 73 of Stock.java

物件區

company1company2

symbol

4

9.62sharePrice

“XYZ”

symbol

5

9.62sharePrice

“XYZ”

equals

equals object2status

在這個當下 (line 73 of Stock.java) ，請問程式可以存取哪幾區的記憶體？

(A) company1 in main()(B) 上方物件的 symbol 欄位(C) 下方物件的 symbol 欄位(D) object2 in equals()

main

sharePrice == object2.sharePrice // line 74

物件區

company1company2

symbol

4

9.62sharePrice

“XYZ”

symbol

5

9.62sharePrice

“XYZ”

equals

object2status

課堂實作• Do Algorithm Workbench 1 (pp. 577-8)– toString: 傳回半徑與面積– equals: 面積相同則代表相同

• Open Labs\CircleDemo.java• 解答： LabAnswers\CircleDemo_ans.java

SECTION 8.8 THE THIS REFERENCE VARIABLE

(p. 556)

main

this物件區

company1company2

symbol

9.62sharePrice

“XYZ”

this5

this

• 可用於所有 non-static 方法中– 試著在 Stock.java 中 #73, #74 加上 this

• if (this.symbol.equals(object2.symbol) &&

– 如果這樣呢 ?• if (this.symbol.equals(this.object2.symbol) &&

• 常見用法– 避免遮蔽效應 (p. 557)

• Run Lab8_4.java

– 呼叫建構式 (p. 558)• Run Lab8_5.java• 相關限制 ( 課本 p. 558)• Compile Lab8_6b.java, Lab8_6a.java

8.7 AGGREGATION(P. 543)

到目前為止，我們自己寫的類別，都是用來修飾區域變數的型態…

課本 p. 551

Aggregation

• Read Instructor.java ( 課本 p. 544)

– 建構式的兩種不同寫法• Read TextBook.java ( 課本 p. 546)

• Read Course.java ( 課本 p. 548)

– 建構式• instructor = new Instructor(instr); (#27 @Course.java)• textBook = new TextBook(text); (#31 @Course.java)

– getInstructor()• return new Instructor(instructor); (#53 @Course.java)

– toString(): 4 個 \n 符號為何印出 9 行 ?• Read CourseDemo.java ( 課本 p. 550)

main

Course myCourse = new Course("Intro to Java", myInstructor, // #20 @CourseDemo.java (p. 550) myTextBook);

myInstructor

myTextBook

4

“Kramer”

“Shawn”

“RH3010”

4

“Starting…”

“Gaddis”“Addison…

”

myCourse

courseName

4

instructor

textBookCourse

Course(String, Instructor, TextBook)

Course myCourse = new Course("Intro to Java", myInstructor, myTextBook);

"Intro to Java”name

instr

4

“Kramer”

“Shawn”

“RH3010”

4

“Starting…”

“Gaddis”“Addison…

”

text

courseName

4

instructor

textBookCourse

Course(String, Instructor, TextBook)

courseName = name;

"Intro to Java”name

instr

4

“Kramer”

“Shawn”

“RH3010”

4

“Starting…”

“Gaddis”“Addison…

”

text

"Intro to Java”courseName

4

instructor

textBookCourse

Course(String, Instructor, TextBook)

instructor = new Instructor(instr);

"Intro to Java”name

instr

3

“Kramer”

“Shawn”

“RH3010”

4

“Starting…”

“Gaddis”“Addison…

”

text

"Intro to Java”courseName

4

instructor

textBookCourse

Instructor

3Instructor

Instructor (Instructor)

lastName = object2.lastName;firstName = object2.firstName;officeNumber = object2.officeNumber;

object23

“Kramer”

“Shawn”

“RH3010”

4

“Starting…”

“Gaddis”“Addison…

”

"Intro to Java”courseName

4

instructor

textBookCourse

Instructor

3

“Kramer”

“Shawn”

“RH3010”

Instructor

Instructor (Instructor)

}

object23

“Kramer”

“Shawn”

“RH3010”

4

“Starting…”

“Gaddis”“Addison…

”

"Intro to Java”courseName

4

instructor

textBookCourse

Instructor

3

“Kramer”

“Shawn”

“RH3010”

Instructor

Return to …

Course(String, Instructor, TextBook)

instructor = new Instructor(instr); // #27 (p. 548)

"Intro to Java”name

instr

4

“Kramer”

“Shawn”

“RH3010”

4

“Starting…”

“Gaddis”“Addison…

”

text

"Intro to Java”courseName

4

instructor

textBookCourse

3

“Kramer”

“Shawn”

“RH3010”

Instructor

Course(String, Instructor, TextBook)

textBook = new TextBook(text); // #31 (p. 548)

"Intro to Java”name

instr

4

“Kramer”

“Shawn”

“RH3010”

4

“Starting…”

“Gaddis”“Addison…

”

text

"Intro to Java”courseName

4

instructor

textBook4

“Kramer”

“Shawn”

“RH3010”

“Starting…”

“Gaddis”“Addison…

”4

Course

Course(String, Instructor, TextBook)

} // #32 (p. 548)

"Intro to Java”name

instr

4

“Kramer”

“Shawn”

“RH3010”

4

“Starting…”

“Gaddis”“Addison…

”

text

"Intro to Java”courseName

4

instructor

textBook4

“Kramer”

“Shawn”

“RH3010”

“Starting…”

“Gaddis”“Addison…

”4

Return to …main

Course

main

Course myCourse = // #19 (p. 550) new Course("Intro to Java", myInstructor, myTextBook);

myInstructor

myTextBook

4

“Kramer”

“Shawn”

“RH3010”

4

“Starting…”

“Gaddis”“Addison…

”

myCourse

4

“Kramer”

“Shawn”

“RH3010”

“Starting…”

“Gaddis”“Addison…

”4

"Intro to Java”courseName

5

instructor

textBook

Aggregation

• Run Lab8_7.java– 請注意 #25– myInstructor 與 myCourse 所包含的 instructor 是

同一物件 ?

課堂實作• 續 Lab8_7.java• 請修改 Course.java 的某一行• 讓輸出結果改成：

• 解答請見 LabAnswers\Course_ans.java

課堂實作• Open Mate\Dog.java, Cat.java,

MateDemo.java, Mate.java• 狗狗跟貓咪可以配成好友 (Mate)• 已知 MateDemo.java 執行後印出：

課堂實作• 請寫出 Mate 類別的各方法– public Mate(Dog d, Cat c)

• 複製狗狗 d 與貓咪 c ，成為 Mate 物件的欄位變數– public String toString()

• 印出“狗狗 :狗狗名字 (年齡 ) 跟貓咪 :貓咪名字 (年齡 ) 是好朋友 "

– public void changeMate(Dog d)• 複製狗狗 d 給 dogMate 欄位變數

– public void changeMate(Cat c)• 複製貓咪 c 給 catMate 欄位變數

• 解答請見 LabAnswers\Mate_ans.java

SECTION 8.9 ENUMERATED TYPES課本 p. 559

要怎麼表示星期幾• int day = 0; // 星期天• int day1 = 1; // 星期一• int day2 = 2; // 星期二• …• int dayN = 8; // 星期 ?

列舉型態 (enumerated type)

• 定義型態 ( 課本 P. 559)

enum Day {SUNDAY, MONDAY , TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY}

• 宣告變數Day workday;

• 指定型態值Workday = Day.THURSDAY;

列舉型態 (enumerated type)

• 列舉型態值是個物件– See Figure 8-15 ( 課本 p. 560)

• Run EnumDemo.java ( 課本 p. 562)

– 假設 X 是一個列舉型態參考變數 ( 物件 ) ，則– System.out.println(X); // 印出列舉型態值– X.ordinal() X 參考的列舉型態值的順位

• Run SportsCarDemo.java (p. 565)

– (with SportsCar.java, CarType.java, CarColor.java)• Run SportsCarDemo2.java (p. 566)

– 注意 case 敘述後不接列舉型態 (CarType)

SECTION 9.2 PASSING OBJECTS AS ARGUMENTS TO METHODS

PASSOBJECT.JAVA(P. 570)Section 9.2

main

Rectangle box = new Rectangle (12.0, 5.0); // line 10

物件區

box

12.0length

5.0width

main

displayRectangle (r); // line 14

物件區

box

12.0length

5.0width

displayRectangler

main

System.out.println(“Length : “ + r.getLength() + “Width : “ + r.getWidth()); // line 27-28

物件區

box

12.0length

5.0width

getLength

displayRectangler

PASSOBJECT2.JAVA(P. 572)Section 9.2

main

Rectangle box = new Rectangle (12.0, 5.0); // line 11

物件區

box

12.0length

5.0width

main

displayRectangle (r); // line 20

物件區

box

12.0length

5.0width

displayRectangler

main

r.setLength(0.0) ; // line 37

物件區

box

0.0length

5.0width

setLength

displayRectangler

0.0

main

r.setWidth(0.0) ; // line 38

物件區

box

0.0length

0.0width

setWidth

displayRectangler

0.0

把物件傳入方法可以改變物件欄位值

SECTION 9.3 RETURNING OBJECTS FROM METHODS

RETURNOBJECT.JAVA(P. 573)Section 9.3

main

account = getAccount(); // line 15

物件區

account

main

return new BankAccount(balance); // line 44

物件區

account

3200.0balance

getAccountinput

3200.0balance“3200.00”

main

return new BankAccount(balance); // line 44account = getAccount(); // line 15

account

getAccountinput

balance

物件區

3200.0balance

“3200.00”