构造器初始化（二）： base让派生类构造器调用基类中属于自己的构造器

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace InitialConstruct
{
    class BaseClass
    {
        public BaseClass()
        {
            Console.WriteLine("[BaseClass.BaseClass] " + "Construct called");
        }
        public BaseClass(int foo)
        {
            Console.WriteLine("[BaseClass.BaseClass(int foo)]" + " foo={0}", foo);
        }
    }
    class DerivedClass : BaseClass
    {
       

        public DerivedClass()
        {
            Console.WriteLine("[DerivedClass.Derived] " + "Construct called");
        }  
        //如果不用base关键字指定，相当于指定了基类构造器中无参构造器
        public DerivedClass(int foo)
        {
            Console.WriteLine("[DerivedClass.DerivedClass] " + "foo={0}", foo);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("[Main] Instantianting a " + "DerivedClass object");
            DerivedClass derived = new DerivedClass();
            DerivedClass derivedParamer = new DerivedClass(42);
            Console.ReadKey();
        }
    }
}

　　　　　　

使用base关键字指定自己需要的基类构造器：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace InitialConstruct
{
    class BaseClass
    {
        public BaseClass()
        {
            Console.WriteLine("[BaseClass.BaseClass] " + "Construct called");
        }
        public BaseClass(int foo)
        {
            Console.WriteLine("[BaseClass.BaseClass(int foo)]" + " foo={0}", foo);
        }
    }
    class DerivedClass : BaseClass
    {      
        public DerivedClass()
        {
            Console.WriteLine("[DerivedClass.Derived] " + "Construct called");
        }  
        //如果不用base关键字指定，相当于指定了基类构造器中无参构造器
        public DerivedClass(int foo):base(foo)
        {
            Console.WriteLine("[DerivedClass.DerivedClass] " + "foo={0}", foo);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("[Main] Instantianting a " + "DerivedClass object");
            DerivedClass derived = new DerivedClass();
            DerivedClass derivedParamer = new DerivedClass(42);
            Console.ReadKey();
        }
    }
}

总结：

       BaseClass中有两个构造器：一个无参构造器，一个有int参数的构造器。而DerivedClass只有一个构造器，它有一个int参数。如果不用base关键字，DerivedClass将调用无参构造器，这不是我们希望的结果。如何确保能调用到所需的BaseClass构造器？，办法就是：在初始化器列表中显示第告诉编译器希望调用哪个构造器。