基础构造函数的目的是什么 [英] What is the purpose of base constructors

问题描述

在为派生类创建构造函数时调用基础构造函数的目的是什么？



示例：

What is the purpose of calling a base constructor when creating a constructor for a derived class?

Example:

class Manager : Employee
    {
        public Manager()
            :base()
        {
            
        }

推荐答案

基础构造函数允许在构造派生类时执行公共初始化代码。 当您想在构造派生类时向其传递参数时，显式调用基础构造函数。 例如：

A base constructor allows common initialization code to be executed when a derived class is constructed.  You explicitly call a base constructor when you want to pass arguments to it when the derived class is being constructed.  For example:

public class MyException : Exception
{
    public MyException
        (string message,
         object data) : base (message)
    {
        // Common initialization comes here
        ...
    }
}

/ ravi

在你的例子中没有。在这种情况下，将自动调用 Employee 的构造函数。



但是，如果你有一个带参数的构造函数，有一个目的。请考虑以下示例：

In your example none. In this case Employee's constructor will automatically be called.

However, if you have a constructor with parameters, there is a purpose. Consider the following example:

abstract class Foo
{
    protected Foo()
    {
    }

    protected Foo(int number)
    {
    }

    protected Foo(string s)
    {
    }
}

class Bar : Foo
{
    public Bar()
    {
        // Foo() is invoked automatically, since the call to the base constructor is omitted.
    }

    public Bar(int number)
        : base(number)
    {
        // Foo(int) is called, since it is explicitly invoked
    }

    public Bar(string s)
    {
        // Foo() is invoked automatically, since the call to the base constructor is omitted.
    }
}

如果 Foo 不有一个默认的构造函数（在我的例子中），它的构造函数需要显式调用。如果你没有在 Bar 上实现 some 构造函数，实际上会出现编译器错误，如果你没有调用基础构造函数，那么也将是一个错误。



底线，如果您的基类中有无参数构造函数，如果您没有明确指定它，它将自动调用。如果你没有无参数构造函数，你有从派生类中调用它，无论你是否需要它。

If Foo does not have a default constructor (in my example it does), its constructor needs to be explicitly called. There will actually be a compiler error if you don't implement some constructor on Bar, and if you don't call the base constructor, there will be an error as well.

Bottom line, if you have a parameterless constructor in your base class, it will be automatically called if you don't explicitly specify it. And if you do not have a parameterless constructor, you have to call it from your derived class whether you want it or not.

base constructor用于运行基类方法

base constructor is used for run base class methods

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