实例构造与结构构造(Java/C#)

所谓实例构造就是指通常的构造函数带参数的和不带参数的，其中不带参数的构造函数又叫做默认构造函数。而类型构造函数又可称为静态构造函数。例如：

public class Customer...{
      public Customer()...{ ... }   // instance constructor, default
      public Customer(Type type)...{ ... } //instance constructor with argument
      static Customer()...{ ... }   // type constructor
}

其中public Customer(),public Customer(Type type),为实例构造函数，static Customer为类型构造函数，当实例化一个这样的类的时候如：Customer customer = new Customer([Type type])时，CLR首先会调用类型构造函数，然后是实例构造函数。下面看个例子：

public class Customer : Base ...{
     public Customer()...{
           System.Console.WriteLine("Customer instance constructor was invoked.");
      }
      static Customer()...{
            System.Console.WriteLine("Customer type constructor was invoked.");
      }
}
public class Base...{
      public Base()...{
           System.Console.WriteLine("Base instance constructor was invoked.");
      }
      static Base()...{
           System.Conole.WriteLine("Base type constructor was invoked.");
      }
}

到创建Customer对象时候，customer = new Customer();时候有如下输出：

Customer type constructor was invoked.

Base type constructor was invoked.

Base instance was invoked.

Customer instance was invoked.

而在Java中却不一样，看下面的例子：

package mf;
public class Base ...{
    public Base()...{
        System.out.println("Base instance constructor was invoked.");
    }
    static...{
        System.out.println("Base type constructor was invoked.");
    }
}
public class Customer extends Base...{
    public Customer()...{
        System.out.println("Customer instance constructor was invoked.");
    }
    static...{
        System.out.println("Customer type constructor was invoked.");
    }
}
public class Test ...{
    public static void main(String[] args) ...{
        Customer customer = new Customer();
    }

}

其输出结果为：

Base type constructor was invoked.
Customer type constructor was invoked.
Base instance constructor was invoked.
Customer instance constructor was invoked.