OOP with Java 通知 Project 4: 5 月 2 日晚 9 点

Size: px

Start display at page:

Download "OOP with Java 通知 Project 4: 5 月 2 日晚 9 点"

运爱禹
6 years ago
Views:

1 OOP with Java Yuanbin Wu

2 OOP with Java 通知 Project 4: 5 月 2 日晚 9 点

3 复习 Java 包创建包 : package 语句, 包结构与目录结构一致使用包 : import restaurant/ - people/ - Cook.class - Waiter.class - tools/ - Fork.class - Table.class import restaurant.people.cook; import restaurant.tools.fork; import restaurant.tools.*; import restaurant.*;

4 复习访问控制对类的成员 ( 数据, 方法 ) 的一种修饰对哪些外部对象是可见的? package access (default package), public, private, protected Class B Class A Class C package access private public protected unless... Package 1 Package 2

5 复习为什么需要访问控制? 封装将易变的与稳定的部分区分开在满足需求的情况下, 接口尽量简单

6 OOP with Java 类的复用组合继承组合与继承

7 类的复用类的复用 (reuse classes) 问题 : 如何通过已有类来定义新的类已有类 A, 创建类 B B 有部分功能与 A 重合例子已有 Car 类, 创建 Transformer 类?

8 类的复用 class A { // data //... // methods // Copy and Paste class B { // data of A //... // methods of A // // new things

9 类的复用情况 1 class B 中包含 class A 类型的数据成员例如 : 引擎类 : class Engine Car 轮胎类 : class Wheel 离合器类 : class Clutch 汽车类? has-a 关系 Engine engine; Wheel wheels[4]; Clutch clutch; 组合 (composition)

10 类的复用情况 2 class B 带有 class A 所有的数据和方法成员, 同时增加新的成员, 或者修改原有的成员例如 : 跑车类具有汽车类的所有方法 is-a 关系 A cat is an animal A dog is an animal Cat eat() sleep() Animal Dog eat() sleep() eat() sleep() 继承 (Inheritance)

11 类的复用重复使用已有类的两种方式组合 (composition) 继承 (inheritance)

12 组合将已有类的对象作为新类的数据成员 class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; public class MyCompType { private MyType m = new MyType(); private String s; public MyCompType(){ s = new String( Hello );

13 组合初始化 ( 复习 ) 默认初始化 (null) 定义时初始化构造函数初始化用时初始化当需要使用该成员时再初始化

14 组合一种常见的重用方式广义的说, MyType 类可视为对基本类型的重用 class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; class MyType { public Integer i; public Double d; public Character c; private String s; private Random r; private Picture p; public void set(double x) { d = x; public double get() { return d;

15 继承新类包含已有类的方法和数据, 并可修改 / 增添语法 : extends A 称为父类 (super class) 或基类 (base class) B 称为子类 (sub-class) class A{ A public class B extends A { B

16 继承 1. 子类有父类的所有方法和数据. class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; public class MySubType extends MyType{ public static void main(string [ ]args){ MySubType ms = new MySubType(); ms.set(1.0); System.out.println(ms.get()); System.out.println(ms.i);

17 继承 2. 子类可以定义新的方法和数据. class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; public class MySubType extends MyType{ String s = new String( Hello ); public double add(double d){ return this.d + d; public double add(string s){ return this.s + s; public static void main(string [ ]args){ MySubType ms = new MySubType(); System.out.println(ms.get()); System.out.println(ms.add(1.0)); System.out.println(ms.add( World ));

18 继承 3. 子类可以更新父类的方法, 称为重写 (overriding) class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; public class MySubType extends MyType{ public void set(double x){ i = (int)x; public double get() { return i; public static void main(string [ ]args){ MySubType ms = new MySubType(); ms.set(1.0); System.out.println(ms.get()); System.out.println(ms.i); System.out.println(ms.d);

19 继承继承的基本功能子类有父类的所有方法和数据子类可以定义新的方法和数据子类可以重写 (override) 父类的方法

c; public void set(double x) { d = x; public double get() { return d; COPY public class

20 继承当定义一个子类时发生了什么? 可能性 1: copy&paste 父类的接口和数据, 创建一个新的类 class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; COPY public class MySubType { /* public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; */ public string s; public childmethods() {...

void set(double x) { d = x; public double get() { return d; COMPOSITION

21 继承当定义一个子类时发生了什么? 可能性 2: 创建一个新的类, 包含一个父类的对象作为数据成员 ( 组合!) class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; COMPOSITION public class MySubType { /* public MyType m; */ public string s; public childmethods() {...

22 继承 super 关键字子类的对象包含一个隐藏的父类对象在子类中, super 为该父类对象的引用复习 : this 关键字 public class MySubType extends MyType{ /* MyType _this; MySubType _super; */ public string s; public childmethods() {... 作用当方法被重写时, 可以通过 super 调用父类的方法

23 继承构造函数在子类构造函数调用前, 首先调用父类构造函数 class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; public MyType(){ System.out.println( In base class ); public class MySubType extends MyType{ public MySubType (){ System.out.println( In sub class ); public static void main(string [ ]args){ MySubType ms = new MySubType(); class MySubSubType extends MySubType{ public MySubSubType (){ System.out.println( In sub sub class );

24 继承构造函数调用父类带参数的构造函数必须出现在子类构造函数的首行 class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; public MyType(){ System.out.println( In base class ); public MyType(double d){ this.d = d; public class MySubType extends MyType{ public MySubType (){ super(1.0); System.out.println( In sub class ); public static void main(string [ ]args){ MySubType ms = new MySubType();

25 例子 public class Circle { public double radius; public String color; public Circle() { this.radius = 1.0; this.color = "red"; public Circle(double radius) { this.radius = radius; this.color = "red"; public Circle(double radius, String color) { this.radius = radius; this.color = color; // Return the area of this Circle public double getarea() { return radius * radius * Math.PI; public String tostring() { return "This is a Circle"; public class Cylinder extends Circle { public double height; public Cylinder() { super(); this.height = 1.0; public Cylinder(double height) { super(); this.height = height; public Cylinder(double height, double radius) { super(radius); this.height = height; public Cylinder(double height, double radius, String color) { super(radius, color); this.height = height; // Return the volume of this Cylinder public double getvolume() { return super.getarea()*height; // Use Circle's getarea() // overriding public double getarea() { return 2 * radius * Math.PI*height + 2*super.getArea(); public String tostring() { return "This is a Cylinder";

26 例子 public class Bicycle { public int cadence; public int gear; public int speed; // constructor public Bicycle(int startcadence, int startspeed, int startgear) { gear = startgear; cadence = startcadence; speed = startspeed; public class MountainBike extends Bicycle { public void setcadence(int newvalue) { cadence = newvalue; public void setgear(int newvalue) { gear = newvalue; public void applybrake(int decrement) { speed -= decrement; public void speedup(int increment) { speed += increment; // the MountainBike subclass adds one feld public int seatheight; // the MountainBike subclass has one constructor public MountainBike(int startheight, int startcadence, int startspeed, int startgear) { super(startcadence, startspeed, startgear); seatheight = startheight; // the MountainBike subclass adds one method public void setheight(int newvalue) { seatheight = newvalue;

27 继承不同类之间通过父类 - 子类关系构成一棵树

28 继承 Object class 每个类都是 Object class 的子类 Single root class hierarchy tree tostring(), equals(),.. Let s try Object B MyType A MySubType

29 继承重写 (override) 子类重新实现父类的方法 ( 同一个函数 ) 重载 (overload) 相同函数名, 不同参数列表

30 继承例子 class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public void set(int y) {i = y; public double get() { return d; public class MySubType extends MyType{ public void set(double x){ i = (int)x; public void set(char z) {c = z; public static void main(string [ ]args){ MySubType ms = new MySubType(); ms.set(1.0); System.out.println(ms.get()); System.out.println(ms.i); System.out.println(ms.d);

31 继承例子 class MyType { public int i; public double d; public char c; private void set(double x) { d = x; private void set(int y) {i = y; public double get() { return d; public class MySubType extends MyType{ public void set(double x){ i = (int)x; public void set(char z) {c = z; public static void main(string [ ]args){ MySubType ms = new MySubType(); ms.set(1.0); System.out.println(ms.get()); System.out.println(ms.i); System.out.println(ms.d);

32 组合与继承 class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; public class MyCompType { private MyType m = new MyType(); private String s; public MyCompType(){ s = new String( Hello ); public class MySubType extends MyType{ public static void main(string [ ]args){ MySubType ms = new MySubType(); ms.set(1.0); System.out.println(ms.get()); System.out.println(ms.i);

33 组合与继承同时使用组合与继承 public class MySubType extends MyType{ String s = new String( Hello ); public static void main(string [ ]args){ MySubType ms = new MySubType(); ms.set(1.0); System.out.println(ms.get()); System.out.println(ms.i);

34 组合与继承比较 B, C 对象都包含一个 A 的对象访问方式不同 b.a.get(); b.a.set(1); c.get(); c.set(1); 设计角度 : 类间关系不同 has-a 关系 is-a 关系 class A{ public get(){ public set(int i){ class B{ public A a = new A(); class C extends A {

35 组合与继承没有 is-a 关系, 但需能调用另一类的所有方法 class SpaceShipControls{ void up(int v) { void down(int v) { void left(int v) { void right(int v) { void forward(int v) { void backward(int v) { class SpaceShip extends SpaceShipControls{ Static public void main(string []args){ SpaceShip s = new SpaceShip(); s.up(); s.forward(); 代理 (Delegation) 介于组合与继承之间 class SpaceShip { Private SpaceShipControls s; public void up() {s.up(); public void down() {s.down(); public void left() {s.left(); public void up() {s.right(); public void forward() {s.forward(); public void backward() {s.backward();

36 总结组合类 B 包含类 A 作为数据成员 has-a 继承类 B 具有类 A 的所有数据与方法, 并能增添修改 Is-a 方法重写 (override)

OOP with Java 通知 Project 3: 3 月 29 日晚 9 点 4 月 1 日上课

OOP with Java Yuanbin Wu cs@ecnu OOP with Java 通知 Project 3: 3 月 29 日晚 9 点 4 月 1 日上课复习 Java 包创建包 : package 语句, 包结构与目录结构一致使用包 : import restaurant/ - people/ - Cook.class - Waiter.class - tools/ - Fork.class