用类做的类型转换是什么意思？

[proyeah]

《C#入门经典》第十一章1.1代码

using System;

namespace Ch11Ex01
{
	/// <summary>
	/// Summary description for Animal.
	/// </summary>
   
      public abstract class Animal
      {
         protected string name;

         public string Name
         {
            get
            {
               return name;
            }
            set
            {
               name = value;
            }
         }

         public Animal()
         {
            name = "The animal with no name";
         }

         public Animal(string newName)
         {
            name = newName;
         }

         public void Feed()
         {
            Console.WriteLine("{0} has been fed.", name);
         }
      }
      public class Cow : Animal
      {
         public void Milk()
         {
            Console.WriteLine("{0} has been milked.", name);
         }

         public Cow(string newName) : base(newName)
         {
         }
      }

      public class Chicken : Animal
      {
         public void LayEgg()
         {
            Console.WriteLine("{0} has laid an egg.", name);
         }

         public Chicken(string newName) : base(newName)
         {
         }
      }
   

}

using System;
using System.Collections;

namespace Ch11Ex01
{
	/// <summary>
	/// Summary description for Class1.
	/// </summary>
	class Class1
	{
		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main(string[] args)
		{
         Console.WriteLine("Create an Array type collection of Animal " +
            "objects and use it:");
         
         Animal[] animalArray = new Animal[2];
         Cow myCow1 = new Cow("Deirdre");
         animalArray[0] = myCow1;
         animalArray[1] = new Chicken("Ken");
         
         foreach (Animal myAnimal in animalArray)
         {
            Console.WriteLine("New {0} object added to Array collection, " +
               "Name = {1}", myAnimal.ToString(), myAnimal.Name);
         }
         
         Console.WriteLine("Array collection contains {0} objects.",
            animalArray.Length);
         animalArray[0].Feed();
         ((Chicken)animalArray[1]).LayEgg();
         Console.WriteLine();

         Console.WriteLine("Create an ArrayList type collection of Animal " +
            "objects and use it:");
         ArrayList animalArrayList = new ArrayList();
         Cow myCow2 = new Cow("Hayley");
         animalArrayList.Add(myCow2);
         animalArrayList.Add(new Chicken("Roy"));
         
         foreach (Animal myAnimal in animalArrayList)
         {
            Console.WriteLine("New {0} object added to ArrayList collection," +
               " Name = {1}", myAnimal.ToString(), myAnimal.Name);
         }
         Console.WriteLine("ArrayList collection contains {0} objects.",
            animalArrayList.Count);
         ((Animal)animalArrayList[0]).Feed();
         ((Chicken)animalArrayList[1]).LayEgg();
         Console.WriteLine();

         Console.WriteLine("Additional manipulation of ArrayList:");
         animalArrayList.RemoveAt(0);
         ((Animal)animalArrayList[0]).Feed();
         animalArrayList.AddRange(animalArray);
         ((Chicken)animalArrayList[2]).LayEgg();
         Console.WriteLine("The animal called {0} is at index {1}.",
            myCow1.Name, animalArrayList.IndexOf(myCow1));
         myCow1.Name = "Janice";
         Console.WriteLine("The animal is now called {0}.",
            ((Animal)animalArrayList[1]).Name);

		}
	}
}

在class类中，有这样的语句
animalArray[0].Feed();
((Chicken)animalArray[1]).LayEgg();
问题一：为什么第一个语句不用类型，而第二个要呢
问题二：用类来做类型和用类来做类型转换是什么意思，是不是和结构类似？
问题三：怎样才能用类做类型转换？
问题四：怎样书上都没说过这个问题呢？是我看漏了吗？

[fengjian_428]

1 因为Chicken子类和animal父类都有Feed方法 而LayEgg方法只有Chicken子类具有
2 不是。 一定要有继承关系才可以转换
3 class A{} class B:A{} B继承于A 就可以转换了 A A1=new B(); B A2=(B)A1;类似于这样
4 估计是你看漏了

[懦芞]

up

[xiaojia19850414]

占位学习。

[jimh]

up

[yuanhuiqiao]

这里面有一定的解耦思想

[微创社（MCC）]

简单工厂模式

说明:继承的is-a关系

包括隐式转换,如:(Chicken)animalArray[1]等
myAnimal.Name则体现了基类的抽象功能

[hecker728]

1,animalArray是父类对象。animalArray[0]对象的引用指向Cow类的对象，animalArray[１]对象的
　引用指向Chicken类的对象。因为Cow类继承类父类的Feed()方法，所以可以直接
animalArray[0].Feed(); 这样调用，而LayEgg(); 是子类Chicken特有的方法，父类没有，所以要转换。

2,类是引用类型，结构是值类型。面向对象的变成中，我们要访问某个类的成员的时候，要通过　对象.成员
这种方式来访问，那么这个对象就是由类来定义的。

3,类的继承中，当我们初始化一个父类对象。那么该父类对象可以通过类型转换，来转换为任何其子类的对象

4,可能书上是用其他方式来表达的，你没注意到。