面向对象第五章继承和多态.ppt

1、第5章 继承和多态,5.1继承,基类和派生类 自顶向下的分解 自底向上的抽象,图形,飞机,汽车,轮船,交通工具,5.1继承,基类和派生类 .NET类库,5.1继承,派生类的定义,public class Automobile private float speed = 100; public float Run(float distance) return distance/speed; public class Bus : Automobile ,5.1继承,派生类的使用,public static void Main() Automobile a1 = new Automobile();

2、a1.Run(1000); Bus b1 = new Bus(); b1.Run(1000); a1 = new Bus(); ,例：P5_1,5.1继承,隐藏基类成员,public class Automobile protected float speed; protected float weight; public float Run(float distance) return distance/speed; ,5.1继承,隐藏基类成员,public class Car : Automobile public new float Run(float distance) return

3、(1+weight/100) * distance/speed; ,5.1继承,隐藏基类成员 覆盖：根据声明类型决定成员调用,Automobile a1 = new Car(); a1.Run(1000); Car a2 = new Car(); a2.Run(1000);,Automobile.Run,Car.Run,例：P5_2,5.1继承,base关键字,public class Car:Automobile() . Public void ShowSpeed() Console.WriteLine(“理想状态行驶1000千米需要0小时”,base.Run(1000); Console.

4、WriteLine(“行驶1000千米需要0小时”, Run(1000); ,Automobile.Run,Car.Run,public Truck (float speed):base(speed,15) load = 30; ,5.1继承,base关键字,public Truck (float speed):base(speed) load = 30; Weight = 15; ,public Automobile() public Automobile(float speed) this.speed = speed; public Automobile(float speed,float

5、 weight) this.speed = speed; this.weight = weight; ,5.1继承,对象的生命周期,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(),例：P5_3,5.2多态性,If（a1

6、is Bus） Console.WriteLine(“客车行驶1000千米需0小时”,(Bus)a1).Run(1000); else if (a1 is Truck) Console.WriteLine(“客车行驶1000千米需0小时”,(Truck)a1).Run(1000); else Console.WriteLine(“客车行驶1000千米需0小时”,a1.Run(1000);,问题： 假设Bus和Truck类继承Automobile，并且都隐藏了Run方法，如何准确计算某汽车对象a1的行驶时间？,5.2多态性,基类：虚拟成员,public class Automobile prot

7、ected float speed; protected float weight; public virtual float Run(float distance) return distance/speed; ,5.2多态性,派生类：重载成员,public class Truck : Automobile private float load; public override float Run(float distance) return base.Run(1+(load+weight)/100); ,public class Car : Automobile public overri

8、de float Run(float distance) return (1+weight/100) * distance/speed; ,5.2多态性,重载：根据实际类型决定成员调用,Automobile a1 = new Car(); a1.Run(1000); Automobile a2 = new Truck(); a2.Run(1000);,Car.Run,Truck.Run,例：P5_4,5.2多态性,抽象类和抽象方法 抽象类,public abstract class Automobile protected float speed; protected float weight

9、; public float Run(float distance) return distance/speed; ,Automobile a1 = new Automobile();,5.2多态性,抽象类和抽象方法 抽象类,public abstract class Automobile protected float speed; protected float weight; public virtual float Run(float distance) return 0; ,5.2多态性,抽象类和抽象方法 抽象方法,public abstract class Automobile p

10、rotected float speed; protected float weight; public abstract float Run(float distance); ,public class Truck : Automobile private float load; ,5.2多态性,抽象类和抽象方法 抽象方法,public class Truck : Automobile private float load; public override float Run(float distance) return base.Run(1+(load+weight)/100); ,5.2

11、多态性,抽象类和抽象方法 抽象属性和索引函数,public abstract int X get; ,public abstract int thisint index get;set; ,例：P5_5,5.2多态性,密封类,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); ,5.2多态性,密封方法,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 override float Run(float distance) return base.Run(1+(lo