我们应该始终包含在类的默认构造函数？ [英] Should we always include a default constructor in the class?

问题描述

我一直在问这个问题的一位同事说，我们应该始终在一个类中默认的构造函数？如果是这样，为什么呢？如果没有，为什么不呢？

I have been asked this question by a colleague that should we always include a default constructor in a class? If so, why? If no, why not?

示例 的

public class Foo {

    Foo() { }

    Foo(int x, int y) {
        ...
    } 

}

我也有兴趣了解这一部分的灯光专家。

I am also interested to get some lights on this from experts.

推荐答案

您必须记住，如果你不提供一个重载的构造函数，编译器将生成一个默认的构造函数为您服务。这意味着，如果你只是有

You have to keep in mind that if you don't provide an overloaded constructor, the compiler will generate a default constructor for you. That means, if you just have

public class Foo
{ 
} 

，编译器会产生这样的：

The compiler will generate this as:

public class Foo
{ 
    public Foo() { }  
} 

然而，一旦你添加其他构造

However, as soon as you add the other constructor

public class Foo
{ 
    public Foo(int x, int y)
    { 
        // ... 
    }  
} 

编译器将不再自动生成默认的构造函数为您服务。 ，即$;如果类是已经在其他code这依赖于一个默认的构造函数presence，富F =新的Foo（）使用C $ C现在都要碎了。

The compiler will no longer automatically generate the default constructor for you. If the class was already being used in other code which relied on the presence of a default constructor, Foo f = new Foo();, that code would now break.

如果你不希望有人能够初始化类，而不提供数据，您应该创建一个默认的构造函数是私人是明确的事实，你是被无输入数据构建preventing实例。

If you don't want someone to be able to initialize the class without providing data you should create a default constructor which is private to be explicit about the fact that you are preventing instances from being constructed with no input data.

但有时，当有必要提供一个默认的构造函数（公共或私人）。如同pviously提到的$ P $，某些类型的序列化需要一个默认的构造。还有，当一个类具有多个参数化的构造时间，但还需要较低级初始化，在此情况下私人默认的构造可以使用其从参数化的构造链中

There are times, however, when it is necessary to provide a default constructor (whether public or private). As was previously mentioned, some types of serialization require a default constructor. There are also times when a class has multiple parameterized constructors but also requires "lower level" initialization, in which case a private default constructor can be used which is chained in from the parameterized constructors.

public class Foo
{
   private Foo()
   {
      // do some low level initialization here
   }

   public Foo(int x, int y)
      : this()
   {
      // ...
   }

   public Foo(int x, int y, int z)
      : this()
   {
      // ...
   }
}

这篇关于我们应该始终包含在类的默认构造函数？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！