1.此接口用于对集合 的自定义相等比较算法的实现。包含2个方法：
Equals(T,T): 确定指定的对象是否相等。 T 为要比较的对象类型；
GetHashCode(T) :返回指定对象的哈希代码。如果两个对象的Equal 比较结果相等，则他们hashCode返回的对象也必须返回同一个值；
2. 官方建议继承 EqualityComparer<T> 而不是实现 IEqualityComparer<T>
3.
Union()
这个方法将会Union(并集)两个序列(集合)连接成一个新列表(集合)
public static IEnumerable<TSource> Union<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second)
public static IEnumerable<TSource> Union<TSource>(this IEnumerable<TSource> first,IEnumerable<TSource> second, IEqualityComparer<TSource> comparer)
Intersect ()
它将产生两个序列的交集.
方法定义是:
public static IEnumerable<TSource> Intersect<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second) public static IEnumerable<TSource> Intersect<TSource>(this IEnumerable<TSource> first, Enumerable<TSource> second,IEqualityComparer<TSource> comparer)
Except ()
它是从一个集合中删除存在另一个集合中的项.两个序列产生的集合差. 英文意思是：除此之外
方法定义是:
public static IEnumerable<TSource> Except<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second)
public static IEnumerable<TSource> Except<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second, IEqualityComparer<TSource> comparer)
实例代码分别如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
namespace test
{
class Program
{
static void Main(string[] args)
{
IList<Student> oneStudents = new List<Student>();
oneStudents.Add(new Student(1,false,"小新1","徐汇"));
oneStudents.Add(new Student(2,false,"小新2","闵行"));
oneStudents.Add(new Student(3, false, "小新3", "嘉定"));
oneStudents.Add(new Student(4, false, "小新4", "闸北"));
IList<Student> twoStudents = new List<Student>();
twoStudents.Add(new Student(5, false, "小新5", "贵州"));
twoStudents.Add(new Student(6, false, "小新6", "湖北"));
twoStudents.Add(new Student(7, false, "小新7", "山东"));
twoStudents.Add(new Student(8, false, "小新8", "西藏"));
IList<Student> threeStudents = new List<Student>();
threeStudents.Add(new Student(1, false, "小新1", "徐汇"));
threeStudents.Add(new Student(2, false, "小新2", "闵行"));
var bingji = oneStudents.Union(twoStudents, new StudentListEquality()).ToList();//并（全）集
var jiaoji = oneStudents.Intersect(threeStudents, new StudentListEquality()).ToList();//交集
var chaji = oneStudents.Except(threeStudents, new StudentListEquality()).ToList();//差集
Console.WriteLine();
Console.WriteLine("以下是并集的结果");
bingji.ForEach(x =>
{
Console.WriteLine(x.StudentId.ToString() + " " + x.Sex.ToString() + " " + x.Name.ToString()+" "+x.Address.ToString());
});
Console.WriteLine();
Console.WriteLine("以下是交集的结果");
jiaoji.ForEach(x =>
{
Console.WriteLine(x.StudentId.ToString() + " " + x.Sex.ToString() + " " + x.Name.ToString() + " " + x.Address.ToString());
});
Console.WriteLine();
Console.WriteLine("以下是差集的结果");
chaji.ForEach(x =>
{
Console.WriteLine(x.StudentId.ToString() + " " + x.Sex.ToString() + " " + x.Name.ToString() + " " + x.Address.ToString());
});
}
}
public class Student
{
public Student(int studentId, bool sex, String name, String address)
{
this.StudentId = studentId;
this.Sex = sex;
this.Name = name;
this.Address = address;
}
public int StudentId { get; set; }
public bool Sex { get; set; }
public String Name { get; set; }
public String Address { get; set; }
}
public class StudentListEquality : IEqualityComparer<Student>
{
public bool Equals(Student x, Student y)
{
return x.StudentId == y.StudentId;
}
public int GetHashCode(Student obj)
{
if (obj == null)
{
return 0;
}
else
{
return obj.ToString().GetHashCode();
}
}
}
}