IComparable

Posted 2020-10-06

有对象的地方就会存在比较，就像小时候每次拿着考卷回家，妈妈都会问你隔壁的那谁谁谁考了多少分呀。下面我们也来举个简单的例子，就是有几个人的Salary列表。我们根据基本工资来进行罗列：

    class Program
    {
        static void Main(string[] args)
        {
            ArrayList array = new ArrayList();
            array.Add(1100);
            array.Add(1200);
            array.Add(1160);
            array.Sort();
            foreach (var obj in array)
            {
                Console.WriteLine(obj.ToString());
            }
            Console.ReadLine();
        }
    }

 可以发现通过ArrayList.Sort()方法即可完成排序的任务。不过ArrayList这里只能是一个字段的。假如有姓名、工资两个字段，然后根据工资进行排序那么按照现在的情况来看，ArrayList是无法实现的。所以接口IComparable现在可以派上用场了。现在先定义一个实体，并且实现接口IComparable。

public class Salary:IComparable
    {
        /// <summary>

      /// 姓名
        /// </summary>

      public string Name { get; set; }

        /// <summary>

      /// 基本工资
        /// </summary>

      public int BaseSalary { get; set; }

        /// <summary>

      /// 实现IComparable接口
        /// </summary>

      /// <param name="obj"></param>

        /// <returns></returns>

      public int CompareTo(object obj)

        {
            Salary staff = obj as Salary;
            if (BaseSalary > staff.BaseSalary)
            {
                return 1;
            }
            else if (BaseSalary == staff.BaseSalary)
            {
                return 0;
            }
            else
            {
                return -1;
            }
        }
    }

进行排序

                ArrayList array = new ArrayList();
                array.Add(new Salary() { Name = "aehyok", BaseSalary = 12000 });
                array.Add(new Salary() { Name = "Kris", BaseSalary = 11200 });
                array.Add(new Salary() { Name = "Leo", BaseSalary = 18000 });
                array.Add(new Salary() { Name = "Niki", BaseSalary = 20000 });
                array.Sort();
                foreach (Salary obj in array)
                {
                    Console.WriteLine(string.Format("{0} BaseSalary:{1}", obj.Name, obj.BaseSalary));
                }
                Console.ReadLine();

如果未继承Icomparable接口。那么会出现如下错误。

正确的进行排序，结果如下所示

假如现在在Salary类中添加了一个奖金的字段如下

public class Salary:IComparable
    {
        /// <summary>

      /// 姓名

        /// </summary>

      public string Name { get; set; }

        /// <summary>

      /// 基本工资
        /// </summary>

      public int BaseSalary { get; set; }

        /// <summary>

      /// 奖金
        /// </summary>

      public int Bouns { get; set; }

        /// <summary>

        /// 实现IComparable接口

        /// </summary>

        /// <param name="obj"></param>

        /// <returns></returns>

      public int CompareTo(object obj)

        {
            Salary staff = obj as Salary;
            if (BaseSalary > staff.BaseSalary)
            {
                return 1;
            }
            else if (BaseSalary == staff.BaseSalary)
            {
                return 0;
            }
            else
            {
                return -1;
            }
        }
    }

再继续假如，现在又要以Bouns奖金字段进行排序，那应该怎么处理呢？当然修改Salary实体类中继承的接口方法进行处理肯定是没问题了，但是比较麻烦。我们可以采用自定义比较接口IComparer来实现。

    public class BounsComparer:IComparer
    {
        public int Compare(object x, object y)
        {
            Salary s1 = x as Salary;
            Salary s2 = y as Salary;
            return s1.Bouns.CompareTo(s2.Bouns);
        }
    }

然后重新进行排序

                ArrayList array = new ArrayList();
                array.Add(new Salary() { Name = "aehyok", BaseSalary = 12000,Bouns=500 });
                array.Add(new Salary() { Name = "Kris", BaseSalary = 11200,Bouns=400 });
                array.Add(new Salary() { Name = "Leo", BaseSalary = 18000,Bouns=300 });
                array.Add(new Salary() { Name = "Niki", BaseSalary = 20000,Bouns=700 });
                array.Sort(new BounsComparer());
                foreach (Salary obj in array)
                {
                    Console.WriteLine(string.Format("{0} \\tBaseSalary:{1}\\tBouns{2}", obj.Name, obj.BaseSalary,obj.Bouns));
                }
                Console.ReadLine();

结果如下所示

注意，刚才实现接口名字叫IComparable,而自定义的比较器接口是IComparer

如果我们稍有经验，会发现如下函数中的问题

        public int Compare(object x, object y)
        {
            Salary s1 = x as Salary;
            Salary s2 = y as Salary;
            return s1.Bouns.CompareTo(s2.Bouns);
        }

这个函数中进行了转型处理，这是会影响性能的。如果集合中有成千上万个复杂的实体对象，那么进行排序时耗费的时间是巨大的。所以泛型登场，很好的解决了这个问题。

因此以上代码中的ArrayList，可以替换为List<T>,对应的我们就应该实现IComparable<T>和IComparer<T>。

实现的代码如下:  

1、实体类实现接口IComparable<T>  2、自定义比较器实现接口IComparer<T> 3、进行排序的调用

public class Salary:IComparable<Salary>

    {
        /// <summary>

      /// 姓名
        /// </summary>

      public string Name { get; set; }

      /// <summary>

      /// 基本工资
        /// </summary>

      public int BaseSalary { get; set; }

        /// <summary>

      /// 奖金
        /// </summary>

      public int Bouns { get; set; }

        /// <summary>

      /// 实现IComparable接口
        /// </summary>

      /// <param name="obj"></param>

      /// <returns></returns>

      public int CompareTo(Salary other)
        {
            return BaseSalary.CompareTo(other.BaseSalary);
        }
    }

    public class BounsComparer : IComparer<Salary>
    {
        public int Compare(Salary x, Salary y)
        {
            return x.Bouns.CompareTo(y.Bouns);
        }
    }

                List<Salary> array =new List<Salary>();
                array.Add(new Salary() { Name = "aehyok", BaseSalary = 12000,Bouns=500 });
                array.Add(new Salary() { Name = "Kris", BaseSalary = 11200,Bouns=400 });
                array.Add(new Salary() { Name = "Leo", BaseSalary = 18000,Bouns=300 });
                array.Add(new Salary() { Name = "Niki", BaseSalary = 20000,Bouns=700 });
                array.Sort(new BounsComparer());
                foreach (Salary obj in array)
                {
                    Console.WriteLine(string.Format("{0} \\tBaseSalary:{1}\\tBouns{2}", obj.Name, obj.BaseSalary,obj.Bouns));
                }
                Console.ReadLine();

最终结果