Sun Educational Service 第九單元 實作封裝與建構式

Sun Educational Service Module 9, slide 2 of 43 單元概論 單元目標： – 利用封裝 (encapsulation) 來保護資料 – 設計建構式來初始化物件 問題與討論

Sun Educational Service Module 9, slide 3 of 43 使用封裝

Sun Educational Service Module 9, slide 4 of 43 public 修飾子 public int currentFloor=1; public void setFloor(int desiredFloor) {... }

Sun Educational Service Module 9, slide 5 of 43 public 修飾子 範例： 1public class PublicElevator { 2 3 public boolean doorOpen=false; 4 public int currentFloor = 1; 5 6 public final int TOP_FLOOR = 5; 7 public final int BOTTOM_FLOOR = 1; 8}

Sun Educational Service Module 9, slide 6 of 43 public 修飾子 範例： 1public class PublicElevatorTest { 2 3 public static void main(String args[]) { 4 5 PublicElevator pubElevator = new PublicElevator(); 6 7 pubElevator.doorOpen = true; // 乘客進入 8 pubElevator.doorOpen = false; // 關門 9 // 到 0 樓 ( 在大樓底層的下方 ) 10 pubElevator.currentFloor--; 11 pubElevator.currentFloor++; // 到 7 樓 ( 大樓只有 5 層樓 ) 14 pubElevator.currentFloor = 7; 15 pubElevator.doorOpen = true; // 乘客進出 16 pubElevator.doorOpen = false; 17 pubElevator.currentFloor = 1; // 到 1 樓

Sun Educational Service Module 9, slide 7 of pubElevator.doorOpen = true; // 乘客進出 19 pubElevator.currentFloor++; // 電梯移動時，門是開啟的 20 pubElevator.doorOpen = false; 21 pubElevator.currentFloor--; 22 pubElevator.currentFloor--; 23 } 24 } 25

Sun Educational Service Module 9, slide 8 of 43 private 修飾子 private int currentFloor=1; private void calculateCapacity() {... }

Sun Educational Service Module 9, slide 9 of 43 private 修飾子 範例： 1public class PrivateElevator1 { 2 3 private boolean doorOpen=false; 4 private int currentFloor = 1; 5 6 private final int TOP_FLOOR = 5; 7 private final int BOTTOM_FLOOR = 1; 8}

Sun Educational Service Module 9, slide 10 of 43 private 修飾子 範例： 1public class PrivateElevator1Test { 2 3 public static void main(String args[]) { 4 5 PrivateElevator1 privElevator = new PrivateElevator1(); 6 7 /************************************************** 8 * The following lines of code will not compile * 9 * because they attempt to access private * 10 * variables. * 11 **************************************************/ privElevator.doorOpen = true; // 乘客進入 14 privElevator.doorOpen = false; // 關門 15 // 到 0 樓 ( 在大樓底層的下方 ) 16 privElevator.currentFloor--; 17 privElevator.currentFloor++;

Sun Educational Service Module 9, slide 11 of // 到 7 樓 ( 大樓只有 5 層樓 ) 20 privElevator.currentFloor = 7; 21 privElevator.doorOpen = true; // 乘客進出 22 privElevator.doorOpen = false; 23 privElevator.currentFloor = 1; // 到 1 樓 24 privElevator.doorOpen = true; // 乘客進出 25 privElevator.currentFloor++; // 電梯移動時，門是開啟的 26 privElevator.doorOpen = false; 27 privElevator.currentFloor--; 28 privElevator.currentFloor--; 29 } 30 }

Sun Educational Service Module 9, slide 12 of 43 介面 vs. 實作

Sun Educational Service Module 9, slide 13 of 43 介面 vs. 實作 範例： 1public class PrivateShirt1 { 2 3 private int shirtID = 0; // 襯衫的預設 ID 4 private String description = “-description required-”; // 預設 5 6 // 顏色代碼為 R= 紅色， B= 藍色， G= 綠色， U= 未設定 7 private char colorCode = ‘U’; 8 private double price = 0.0; // 所有襯衫的預設價格 9 private int quantityInStock = 0; // 所有襯衫的預設數量 public char getColorCode() { 12 return colorCode; 13 } public void setColorCode(char newCode) { 16 colorCode = newCode; 17 }

Sun Educational Service Module 9, slide 14 of // 其他對 shirtID 、 description 、 price 、和 quantityInStock 20 // 的取得和設定方法，仿照上述的做法 } // 類別結尾

Sun Educational Service Module 9, slide 15 of 43 介面 vs. 實作 範例： 1public class PrivateShirt1Test { 2 3 public static void main (String args[]) { 4 5 PrivateShirt1 privShirt = new PrivateShirt1(); 6 char colorCode; 7 8 // 設定合法的 colorCode 9 privShirt.setColorCode(‘R’); 10 colorCode = privShirt.getColorCode(); // PrivateShirtTest1 類別能夠設定合法的 colorCode 13 System.out.println(“Color Code: “ + colorCode); // 設定不合法的 colorCode 16 privShirt.setColorCode(‘Z’); 17 colorCode = privShirt.getColorCode();

Sun Educational Service Module 9, slide 16 of // PrivateShirtTest1 類別能夠設定不合法的 colorCode 20 System.out.println(“Color Code: “ + colorCode); 21 } 22 }

Sun Educational Service Module 9, slide 17 of 43 介面 vs. 實作 範例： 1public class PrivateShirt2 { 2 3 private int shirtID = 0; // 襯衫的預設 ID 4 private String description = “-description required-”; // 預設 5 6 // 顏色代碼為 R= 紅色， B= 藍色， G= 綠色， U= 未設定 7 private char colorCode = ‘U’; 8 private double price = 0.0; // 所有襯衫的預設價格 9 private int quantityInStock = 0; // 所有襯衫的預設數量 public char getColorCode() { 12 return colorCode; 13 } public void setColorCode(char newCode) { switch (newCode) {

Sun Educational Service Module 9, slide 18 of case ‘R’: 19 case ‘G’: 20 case ‘B’: 21 colorCode = newCode; 22 break; 23 default: 24 System.out.println(“Invalid colorCode. Use R, G, or B”); 25 } 26 } // 其他對 shirtID 、 description 、 price 、和 quantityInStock 29 // 的取得和設定方法，仿照上述的做法 } // 類別結尾

Sun Educational Service Module 9, slide 19 of 43 介面 vs. 實作 範例： 1public class PrivateShirt2Test { 2 3 public static void main (String args[]) { 4 5 PrivateShirt2 privShirt = new PrivateShirt2(); 6 char colorCode; 7 8 // 設定合法的 colorCode 9 privShirt.setColorCode(‘R’); 10 colorCode = privShirt.getColorCode(); // PrivateShirtTest1 類別能夠設定合法的 colorCode 13 System.out.println(“Color Code: “ + colorCode); // 設定不合法的 colorCode 16 privShirt.setColorCode(‘Z’); 17 colorCode = privShirt.getColorCode();

Sun Educational Service Module 9, slide 20 of // PrivateShirtTest2 類別無法設定不合法的 colorCode. 20 // colorCode 仍然是 R 21 System.out.println(“Color Code: “ + colorCode); 22 } 23 }

Sun Educational Service Module 9, slide 21 of 43 一個封裝過的電梯 範例： 1public class PrivateElevator2 { 2 3 private boolean doorOpen=false; 4 private int currentFloor = 1; 5 private int weight = 0; 6 7 final int CAPACITY = 1000; 8 final int TOP_FLOOR = 5; 9 final int BOTTOM_FLOOR = 1; public void openDoor() { 12 doorOpen = true; 13 } public void closeDoor() { 16 calculateCapacity(); 17

Sun Educational Service Module 9, slide 22 of if (weight <= CAPACITY) { 19 doorOpen = false; 20 } 21 else { 22 System.out.println(“The elevator has exceeded capacity.”); 23 System.out.println(“Doorswillremainopenuntilsomeoneexits!”); 24 } 25 } // 事實上，電梯會有重量感測器來檢查電梯中實際的重量， 28 // 但為了將問題簡化，我們只取一個隨機的數目來表示電梯 29 // 中的重量 30 // private void calculateCapacity() { 33 weight = (int) (Math.random() * 1500); 34 System.out.println(“The weight is “ + weight); 35 } public void goUp() { 38 if (!doorOpen) { 39 if (currentFloor < TOP_FLOOR) {

Sun Educational Service Module 9, slide 23 of currentFloor++; 41 System.out.println(currentFloor); 42 } 43 else { 44 System.out.println(“Already on top floor.”); 45 } 46 } 47 else { 48 System.out.println(“Doors still open!”); 49 } 50 } public void goDown() { 53 if (!doorOpen) { 54 if (currentFloor > BOTTOM_FLOOR) { 55 currentFloor--; 56 System.out.println(currentFloor); 57 } 58 else { 59 System.out.println(“Already on bottom floor.”); 60 } 61 }

Sun Educational Service Module 9, slide 24 of else { 63 System.out.println(“Doors still open!”); 64 } 65 } public void setFloor(int desiredFloor) { 68 if ((desiredFloor>=BOTTOM_FLOOR)&&(desiredFloor<=TOP_FLOOR)){ while (currentFloor != desiredFloor) { 71 if (currentFloor < desiredFloor) { 72 goUp(); 73 } else { 76 goDown(); 77 } 78 } 79 } 80 else { 81 System.out.println(“Invalid Floor”); 82 } 83 }

Sun Educational Service Module 9, slide 25 of public int getFloor() { 86 return currentFloor; 87 } public boolean getDoorStatus() { 90 return doorOpen; 91 } 92 } 93

Sun Educational Service Module 9, slide 26 of 43 一個封裝過的電梯 範例： 1public class PrivateElevator2Test { 2 3 public static void main(String args[]) { 4 5 PrivateElevator2 privElevator = new PrivateElevator2(); 6 7 privElevator.openDoor(); 8 privElevator.closeDoor(); 9 privElevator.goDown(); 10 privElevator.goUp(); 11 privElevator.goUp(); 12 privElevator.openDoor(); 13 privElevator.closeDoor(); 14 privElevator.goDown(); 15 privElevator.openDoor(); 16 privElevator.goDown(); 17 privElevator.closeDoor();

Sun Educational Service Module 9, slide 27 of privElevator.goDown(); 19 privElevator.goDown(); int curFloor = privElevator.getFloor(); if (curFloor != 5 && ! privElevator.getDoorStatus()) { 24 privElevator.setFloor(5); 25 } privElevator.setFloor(10); 28 privElevator.openDoor(); 29 } 30 }

Sun Educational Service Module 9, slide 28 of 43 範例輸出結果 The weight is 453 Already on bottom floor. 2 3 The weight is Doors still open! The weight is Already on bottom floor

Sun Educational Service Module 9, slide 29 of 43 練習一：撰寫封裝類別 目標 步驟 討論

Sun Educational Service Module 9, slide 30 of 43 變數有效範圍 (Variable Scope) 範例： 1public class Person2 { 2 3 // 變數 age 有效範圍的開始 4 private int age = 34; 5 6 public void displayName() { 7 8 // 字串 name 有效範圍的開始 9 String name = “Peter Simmons”; 10 System.out.println(“My name is “ + name + “ and I am “ + age ); } // 字串 name 有效範圍的結尾 public String getName () { return name; // 這造成錯誤 17 }

Sun Educational Service Module 9, slide 31 of } // 變數 age 有效範圍結尾

Sun Educational Service Module 9, slide 32 of 43 記憶體中的實體變數及區域變數

Sun Educational Service Module 9, slide 33 of 43 建立建構式 語法： modifiers class ClassName { ConstructorName([arguments]) { code_block; } 範例： 1public class ConstructorShirt1 { 2 3 private int shirtID = 0; // 襯衫的預設 ID 4 private String description = “-description required-”; // 預設 5 6 // 顏色代碼為 R= 紅色， B= 藍色， G= 綠色， U= 未設定 7 private char colorCode = ‘U’; 8 private double price = 0.0; // 所有襯衫的預設價格 9 private int quantityInStock = 0; // 所有襯衫的預設數量

Sun Educational Service Module 9, slide 34 of public ConstructorShirt1(char startingCode) { switch (startingCode) { 14 case ‘R’: 15 case ‘G’: 16 case ‘B’: 17 colorCode = startingCode; 18 break; 19 default: 20 System.out.println(“Invalid colorCode. Use R, G, or B”); 21 } 22 } public char getColorCode() { 25 return colorCode; 26 } 27 } // 類別結尾 28 29

Sun Educational Service Module 9, slide 35 of 43 建立建構式 範例： 1public class ConstructorShirt1Test { 2 3 public static void main (String args[]) { 4 5 ConstructorShirt1 constShirt = new ConstructorShirt1(‘R’); 6 char colorCode; 7 8 colorCode = constShirt.getColorCode(); 9 10 System.out.println(“Color Code: “ + colorCode); 11 } 12 }

Sun Educational Service Module 9, slide 36 of 43 預設建構式 範例： ConstructorShirt constShirt = new ConstructorShirt(); 範例： 1public class DefaultShirt { 2 3 private int shirtID = 0; // 襯衫的預設 ID 4 private String description = “-description required-”; // 預設 5 6 // 顏色代碼為 R= 紅色， B= 藍色， G= 綠色， U= 未設定 7 private char colorCode = ‘U’; 8 private double price = 0.0; // 所有襯衫的預設價格 9 private int quantityInStock = 0; // 所有襯衫的預設數量 public DefaultShirt() { 12 colorCode = ‘R’; 13 } 14

Sun Educational Service Module 9, slide 37 of public char getColorCode() { 16 return colorCode; 17 } 18 } // 類別結尾 19

Sun Educational Service Module 9, slide 38 of 43 覆載建構式 範例： 1public class ConstructorShirt2 { 2 3 private int shirtID = 0; // 襯衫的預設 ID 4 private String description = “-description required-”; // 預設 5 6 // 顏色代碼為 R= 紅色， B= 藍色， G= 綠色， U= 未設定 7 private char colorCode = ‘U’; 8 private double price = 0.0; // 所有襯衫的預設價格 9 private int quantityInStock = 0; // 所有襯衫的預設數量 public ConstructorShirt2() { 12 colorCode = ‘R’; 13 } public ConstructorShirt2 (char startingCode) { switch (startingCode) {

Sun Educational Service Module 9, slide 39 of case ‘R’: 19 case ‘G’: 20 case ‘B’: 21 colorCode = startingCode; 22 break; 23 default: 24 System.out.println(“Invalid colorCode. Use R, G, or B”); 25 } 26 } public ConstructorShirt2 (char startingCode, int startingQuantity) { switch (startingCode) { 31 case ‘R’: 32 colorCode = startingCode; 33 break; 34 case ‘G’: 35 colorCode = startingCode; 36 break; 37 case ‘B’: 38 colorCode = startingCode; 39 break;

Sun Educational Service Module 9, slide 40 of default: 41 System.out.println(“Invalid colorCode. Use R, G, or B”); 42 } if (startingQuantity > 0 || startingQuantity < 2000) { 45 quantityInStock = startingQuantity; 46 } else { 49 System.out.println(“Invalid quantity. Must be > 0 or < 2000”); 50 } 51 } public char getColorCode() { 54 return colorCode; 55 } public int getQuantityInStock() { 59 return quantityInStock; 60 } } // 類別結尾 63

Sun Educational Service Module 9, slide 41 of 43 覆載建構式 範例： 1public class ConstructorShirt2Test { 2 3 public static void main (String args[]) { 4 5 ConstructorShirt2 constShirtFirst = new ConstructorShirt2(); 6 ConstructorShirt2 constShirtSecond = new ConstructorShirt2(‘G’); 7 ConstructorShirt2 constShirtThird = new ConstructorShirt2(‘B’, 1000); 8 9 char colorCode; 10 int quantity; colorCode = constShirtFirst.getColorCode(); 13 System.out.println(“Object 1 Color Code: “ + colorCode); colorCode = constShirtSecond.getColorCode(); 16 System.out.println(“Object 2 Color Code: “ + colorCode);

Sun Educational Service Module 9, slide 42 of colorCode = constShirtThird.getColorCode(); 19 quantity = constShirtThird.getQuantityInStock(); 20 System.out.println(“Object 3 Color Code: “ + colorCode); 21 System.out.println(“Object 3 Quantity on Hand: “ + quantity); 22 } 23 }

Sun Educational Service Module 9, slide 43 of 43 練習二：使用建構式 目標 步驟 討論