对于值类型,如果对象的值相等,则相等运算符 (==) 返回 true,否则返回 false。对于string 以外的引用类型,如果两个对象引用同一个对象,则 == 返回 true。对于 string 类型,== 比较字符串的值。
==操作比较的是两个变量的值是否相等。
equals()方法比较的是两个对象的内容是否一致.equals也就是比较引用类型是否是对同一个对象的引用。
对于值类型的比较,这里就不做描述了,下面讨论引用类型的比较:
首先我们看一段程序
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
namespace ConsoleApplication1
{
class Person
{
private string name;
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
public string Name
{
get { return name; }
set { name = value; }
}
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
public Person(string name)
{
this.name = name;
}
}
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
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));
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
object g = a;
object h = b;
Console.WriteLine(g == h);
Console.WriteLine(g.Equals(h));
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
Person p1 = new Person("jia");
Person p2 = new Person("jia");
Console.WriteLine(p1 == p2);
Console.WriteLine(p1.Equals(p2));
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
Person p3 = new Person("jia");
Person p4 = p3;
Console.WriteLine(p3 == p4);
Console.WriteLine(p3.Equals(p4));
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
Console.ReadLine();
}
}
}
运行程序,会输出什么呢?
答案是 true,true,false,true,false,false,true,true。
为什么会出现这个答案呢?因为值类型是存储在内存中的堆栈(以后简称栈),而引用类型的变量在栈中仅仅是存储引用类型变量的地址,而其本身则存储在堆中。
==操作比较的是两个变量的值是否相等,对于引用型变量表示的是两个变量在堆中存储的地址是否相同,即栈中的内容是否相同。
equals操作表示的两个变量是否是对同一个对象的引用,即堆中的内容是否相同。
而字符串是一个特殊的引用型类型,在C#语言中,重载了string 对象的很多方法方法(包括equals()方法),使string对象用起来就像是值类型一样。
因此在上面的例子中,字符串a和字符串b的两个比较是相等的。
对于object g 和object h 时内存中两个不同的对象,所以在栈中的内容是不相同的,故不相等。而g.equals(h)用的是sting的equals()方法故相等(多太)。如果将字符串a和b作这样的修改:
string a="aa";
string b="aa";
则,g和h的两个比较都是相等的。这是因为系统并没有给字符串b分配内存,只是将"aa"指向了b。所以a和b指向的是同一个字符串(字符串在这种赋值的情况下做了内存的优化)。
对于p1和p2,也是内存中两个不同的对象,所以在内存中的地址肯定不相同,故p1==p2会返回false,又因为p1和p2又是对不同对象的引用,所以p1.equals(p2)将返回false。
对于p3和p4,p4=p3,p3将对对象的引用赋给了p4,p3和p4是对同一个对象的引用,所以两个比较都返回true。
如果我们对person的equals方法重写:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
namespace ConsoleApplication1
{
class Person
{
private string name;
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
public string Name
{
get { return name; }
set { name = value; }
}
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
public Person(string name)
{
this.name = name;
}
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
public override bool Equals(object obj)
{
if (!(obj is Person))
return false;
Person per = (Person)obj;
return this.Name == per.Name;
}
}
}那么p1.equals(p2),就会返回true。
==操作比较的是两个变量的值是否相等。
equals()方法比较的是两个对象的内容是否一致.equals也就是比较引用类型是否是对同一个对象的引用。
对于值类型的比较,这里就不做描述了,下面讨论引用类型的比较:
首先我们看一段程序
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
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运行程序,会输出什么呢?
答案是 true,true,false,true,false,false,true,true。
为什么会出现这个答案呢?因为值类型是存储在内存中的堆栈(以后简称栈),而引用类型的变量在栈中仅仅是存储引用类型变量的地址,而其本身则存储在堆中。
==操作比较的是两个变量的值是否相等,对于引用型变量表示的是两个变量在堆中存储的地址是否相同,即栈中的内容是否相同。
equals操作表示的两个变量是否是对同一个对象的引用,即堆中的内容是否相同。
而字符串是一个特殊的引用型类型,在C#语言中,重载了string 对象的很多方法方法(包括equals()方法),使string对象用起来就像是值类型一样。
因此在上面的例子中,字符串a和字符串b的两个比较是相等的。
对于object g 和object h 时内存中两个不同的对象,所以在栈中的内容是不相同的,故不相等。而g.equals(h)用的是sting的equals()方法故相等(多太)。如果将字符串a和b作这样的修改:
string a="aa";
string b="aa";
则,g和h的两个比较都是相等的。这是因为系统并没有给字符串b分配内存,只是将"aa"指向了b。所以a和b指向的是同一个字符串(字符串在这种赋值的情况下做了内存的优化)。
对于p1和p2,也是内存中两个不同的对象,所以在内存中的地址肯定不相同,故p1==p2会返回false,又因为p1和p2又是对不同对象的引用,所以p1.equals(p2)将返回false。
对于p3和p4,p4=p3,p3将对对象的引用赋给了p4,p3和p4是对同一个对象的引用,所以两个比较都返回true。
如果我们对person的equals方法重写:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
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