C#比较

【摘要】 初学C#，此文章意在记录学习心得
C#是如何比较的，首先看如下程序，p1和p2是两个不同的引用，所以第一次比较输出no same。
p1和p3引用同一段内存空间，所以第二次比较输出same。
    class Program     {         static void Main(string[] args)         {             pers…

初学C#，此文章意在记录学习心得

C#是如何比较的，首先看如下程序，p1和p2是两个不同的引用，所以第一次比较输出no same。

p1和p3引用同一段内存空间，所以第二次比较输出same。

class Program
{
static void Main(string[] args)
{
person p1 = new person { name = “SLH” };
person p2 = new person { name = “SLH” };
person p3 = p1;
if (p1 == p2)
Console.WriteLine(“same”);
else
Console.WriteLine(“no same”);
Console.WriteLine(“!-********************-!”);
if (p1 == p3)
Console.WriteLine(“same”);
else
Console.WriteLine(“no same”);
Console.ReadLine();
}
}
class person
{
public string name;
}

第二段程序使用Equals进行比较，结果相同

class Program
{
static void Main(string[] args)
{
person p1 = new person { name = “SLH” };
person p2 = new person { name = “SLH” };
if (p1 .Equals (p2 ))
Console.WriteLine(“same”);
else
Console.WriteLine(“no same”);
Console.ReadLine();
}
}
class person
{
public string name;
}

第三段程序我们在person类中重写了Equals()方法，通过person类型的name属性来比较两个person对象是否相同，结果输出same

class Program
{
static void Main(string[] args)
{
person p1 = new person { name = “SLH” };
person p2 = new person { name = “SLH” };
if (p1 .Equals (p2 ))
Console.WriteLine(“same”);
else
Console.WriteLine(“no same”);
Console.ReadLine();
}
}
class person
{
public string name;
public override bool Equals(object obj)
{
return this.name .Equals(((person )obj).name );
}
}

那么我们如何比较person类型的数组呢，看下面程序，执行结果no same

class Program
{
static void Main(string[] args)
{
person[] persons1 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}
};
person[] persons2 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}
};
if (persons1 != persons2)
Console.WriteLine(“no same”);
else
Console.WriteLine(“same”);

Console.ReadLine();
}
}
class person
{
public string name;
public override bool Equals(object obj)
{
return this.name.Equals(((person)obj).name);
}
}

c#数组显式实现了IStructuralEquatable接口，使用时需要把数组强制转换为该接口，这个接口用于比较两个数组是否内容相同，例程如下。

IStructuralEquatable接口定义了Equals()方法，方法需传入两个参数，第一个参数为另一个数组，object类型，

第二个参数为IEqualityComparer类型，可以通过EqualityComparer<T>类型的Default属性返回IEqualityComparer接口的一个默认实现，就可以定义如何进行比较了

当然person类中还需重写Equals()方法，程序执行结果为same

使用IStructuralEquatable接口需引用System.Collections命名空间

class Program
{
static void Main(string[] args)
{
person[] persons1 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}
};
person[] persons2 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}
};
if (((IStructuralEquatable)persons1).Equals(persons2, EqualityComparer<person>.Default))
Console.WriteLine(“same”);
else
Console.WriteLine(“no same”);

Console.ReadLine();
}
}
class person
{
public string name;
public override bool Equals(object obj)
{
return this.name.Equals(((person)obj).name);
}
}

此时修改persons2数组，程序运行结果为no same

person[] persons1 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}
};
person[] persons2 ={
new person (){name =”Tom”},
new person (){name =”Jackson”}
};

修改persons2数组，程序运行结果no same

person[] persons1 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}

};
person[] persons2 ={
new person (){name =”SLH”},
new person (){name =”Jackson”},
new person (){name =”SLH”}
};

修改persons2数组，程序运行结果no same

person[] persons1 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}

};
person[] persons2 ={
new person (){name =”Jackson”},
new person (){name =”SLH”}

};

由Default属性返回的IEqualityComparer接口的默认实现，首先检查person类型是否实现了IEquatable <T>接口，如果实现了，就调用IEquatable.Equals()方法，

如果没有实现，就调用Object.Equals()方法，看下面程序A与程序B

程序A，运行结果

IEquatable
no same

class Program
{
static void Main(string[] args)
{
person[] persons1 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}
};
person[] persons2 ={
new person (){name =”Jackson”},
new person (){name =”SLH”}
};
if (((IStructuralEquatable)persons1).Equals(persons2, EqualityComparer<person>.Default))
Console.WriteLine(“same”);
else
Console.WriteLine(“no same”);

Console.ReadLine();
}
}
class person:IEquatable <person >
{
public string name;
public override bool Equals(object obj)
{
Console.WriteLine(“Equals”);
return this.name.Equals(((person)obj).name);
}

public bool Equals(person other)
{
Console.WriteLine(“IEquatable”);
return this.name.Equals(other.name);
}
}

程序B运行结果

Equals
no same

class Program
{
static void Main(string[] args)
{
person[] persons1 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}

};
person[] persons2 ={
new person (){name =”Jackson”},
new person (){name =”SLH”}

};
if (((IStructuralEquatable)persons1).Equals(persons2, EqualityComparer<person>.Default))
Console.WriteLine(“same”);
else
Console.WriteLine(“no same”);

Console.ReadLine();
}
}
class person
{
public string name;
public override bool Equals(object obj)
{
Console.WriteLine(“Equals”);
return this.name.Equals(((person)obj).name);
}
}

当然我们也可以不使用EqualityComparer<T>类型的Default属性返回的默认实现，如下程序定义了equalityComparer类，实现了IEqualityComparer接口

class Program
{
static void Main(string[] args)
{
person[] persons1 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}

};
person[] persons2 ={
new person (){name =”SLH”},
new person (){name =”Jackson”}

};
if (((IStructuralEquatable)persons1).Equals(persons2,new equalityComparer () )) //此处第二个参数传入equalityComparer类的匿名对象
Console.WriteLine(“same”);
else
Console.WriteLine(“no same”);

Console.ReadLine();
}
}
class person
{
public string name;
public override bool Equals(object obj)
{
Console.WriteLine(“Equals-person”);
return this.name.Equals(((person)obj).name);
}
}
class equalityComparer :IEqualityComparer
{

public new bool Equals(object x, object y) //执行if判断时，调用equalityComparer类的Equals()方法，此时传入的两个参数为person类型对象，调用person类型的Equals()方法

//因为数组包含两个元素，所以会调用两次
{
Console.WriteLine(“Equals-equalityComparer”);
return x.Equals(y);
}

public int GetHashCode(object obj)
{
return obj.GetHashCode();
}
}

程序运行结果：

Equals-equalityComparer
Equals-person
Equals-equalityComparer
Equals-person
same

文章来源: blog.csdn.net，作者：十里河畔，版权归原作者所有，如需转载，请联系作者。

原文链接：blog.csdn.net/SLRiver/article/details/116357585