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1、1,第5章 继承和多态,纲要,继承 多态性,2,继承,基类和派生类 自顶向下的分解 自底向上的抽象,3,图形,飞机,汽车,轮船,交通工具,继承,基类和派生类 .NET类库,4,继承,基类和派生类,5,public class Automobile private float speed = 100; public float Run(float distance) return distance/speed; public class Bus : Automobile ,Automobile a1 = new Automobile(); a1.Run(1000); Bus b1 = new B
2、us(); b1.Run(1000);,继承,对象的生命周期 构造 析构,6,public class Vehicle public class Automobile : Vehicle public class Car : Automobile public class Limousine : Car ,new Vehicle(),new Automobile(),new Car(),new Limousine(),Vehicle(),Automobile(), Car(),Limousine(),多态性,基类：普通成员 派生类：覆盖成员,7,public class Automobile
3、protected float speed; protected float weight; public float Run(float distance) return distance/speed; ,public class Car : Automobile public new float Run(float distance) return (1+weight/100) * distance/speed; ,多态性,覆盖：根据声明类型决定成员调用,8,Automobile a1 = new Truck(); a1.Run(1000); Car a2 = new Car(); a2.
4、Run(1000);,Automobile.Run,Car.Run,多态性,基类：虚拟成员,9,public class Automobile protected float speed; protected float weight; public virtual float Run(float distance) return distance/speed; ,多态性,基类：虚拟成员 派生类：重载成员,10,public class Truck : Automobile private float load; public override float Run(float distance
5、) return base.Run(1+(load+weight)/100); ,public class Car : Automobile public override float Run(float distance) return (1+weight/100) * distance/speed; ,多态性,重载：根据实际类型决定成员调用,11,Automobile a1 = new Car(); a1.Run(1000); Automobile a2 = new Truck(); a2.Run(1000);,Car.Run,Truck.Run,多态性,抽象类和抽象方法,12,publi
6、c abstract class Automobile protected float speed; protected float weight; public abstract float Run(float distance); ,Automobile a1 = new Automobile();,抽象类不能创建对象!,多态性,抽象类和抽象方法,13,public class Truck : Automobile private float load; ,非抽象派生类必须为基类的抽象方法提供实现!,多态性,抽象类和抽象方法,14,public class Truck : Automobi
7、le private float load; public override float Run(float distance) return base.Run(1+(load+weight)/100); ,多态性,密封类: 不能再被继承,15,public class BigTruck : Truck ,public sealed class Truck : Automobile private float load; public override float Run(float distance) return base.Run(1+(load+weight)/100); ,多态性,密封
8、方法: 不能再被重载,16,public class BigTruck : Truck public override float Run(float distance) return base.Run(1+2*(load+weight)/100); ,public class Truck : Automobile private float load; public sealed float Run(float distance) return base.Run(1+(load+weight)/100); ,17,本章习题,简述public, protected, private关键字在继承中的作用。 简述覆盖和重载的区别，以及它们各自的适用场合。 属性、索引函数和构造函数可否被虚拟和重载？ 试说说图书馆管理系统中可能存在哪些虚拟和重载的情况？,
