.Equals之间的区别是什么== [英] What is the difference between .Equals and ==

问题描述

（二）和 A == b 值类型，引用的 a.Equals的区别是什么类型和字符串类型？这似乎就像一个== B工作蛮好的字符串，但我想一定要使用良好的编码习惯。

解决方案

从 ：当我应该使用等于当我应该使用== ：

  

equals方法仅仅是一个虚拟的   之一System.Object的定义，和   通过取其类选择覆盖   这样做。 ==操作符是一个   操作者可以通过被重载   类，但通常有   身份的行为。

     

有关引用类型，其中==还没有   被超载，它比较是否   两个引用指的是同   对象 - 这正是   实施的Equals确实在   System.Object的。

     

值类型不提供过载   对于==默认。然而，大多数   由提供的值类型   框架提供自己的过载。   的Equals的默认实现   为一个值类型是由提供   值类型，并使用反射来使   的比较，这使得它   比显著慢   类型具体执行正常   将会。此实现还   电话等于在对引用   内被比较的两个值

 使用系统;

公共类测试
{
    静态无效的主要（）
    {
        //创建两个相同，但不同的弦
        字符串=新的字符串（新的char [] {'H'，'E'，'L'，'L'，'O'}）;
        字符串B =新的字符串（新的char [] {'H'，'E'，'L'，'L'，'O'}）;

        Console.WriteLine（A == B）;
        Console.WriteLine（a.Equals（B））;

        //现在让我们看看使用相同的测试，会发生什么，但
        //有类型的对象变量
        对象C = A;
        物D = B;

        Console.WriteLine（C = D）;
        Console.WriteLine（c.Equals（d）条）;
    }
}
 

这短短的示例程序的结果是

 真
真正
假
真正
 

What is the difference between a.Equals(b) and a == b for value types, reference types, and strings? It would seem as though a == b works just fine for strings, but I'm trying to be sure to use good coding practices.

解决方案

From When should I use Equals and when should I use ==:

The Equals method is just a virtual one defined in System.Object, and overridden by whichever classes choose to do so. The == operator is an operator which can be overloaded by classes, but which usually has identity behaviour.

For reference types where == has not been overloaded, it compares whether two references refer to the same object - which is exactly what the implementation of Equals does in System.Object.

Value types do not provide an overload for == by default. However, most of the value types provided by the framework provide their own overload. The default implementation of Equals for a value type is provided by ValueType, and uses reflection to make the comparison, which makes it significantly slower than a type-specific implementation normally would be. This implementation also calls Equals on pairs of references within the two values being compared.

using System;

public class Test
{
    static void Main()
    {
        // Create two equal but distinct strings
        string a = new string(new char[] {'h', 'e', 'l', 'l', 'o'});
        string b = new string(new char[] {'h', 'e', 'l', 'l', 'o'});

        Console.WriteLine (a==b);
        Console.WriteLine (a.Equals(b));

        // Now let's see what happens with the same tests but
        // with variables of type object
        object c = a;
        object d = b;

        Console.WriteLine (c==d);
        Console.WriteLine (c.Equals(d));
    }
}

The result of this short sample program is

True
True
False
True

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