对象集合如何排序

题目说明：学生类包括成绩、科目和学号，请根据课程成绩grade将学生进行排序。

1.  先创建一个学生类和IComparer接口。

public class Student : IComparable
{
    public double mygrade;
    public string mysubject, myID;
    public Student() { }
    public Student(double grade, string subject, string id)
    {
        mygrade = grade;
        mysubject = subject;
        myID = id;
    }

2.   加入外部比较器

int IComparable.CompareTo(Object obj)
        {
            if (obj is Student)
            {
                Student stu = (Student)obj;
                if (this.mygrade > stu.mygrade) { return -1; }
                else if (this.mygrade < stu.mygrade) { return 1; }
                else { return 0; }
            }
            throw new ArgumentException("object is not a Student");
        }

说明：此比较器排序后为降序数组，因为：如果if (this.mygrade > stu.mygrade) { return -1; }

，意为本类的grade大于外来类的grade，则返回-1（假），则需要交换他们的位置。

如果else if (this.mygrade < stu.mygrade) { return 1; }，意为如果本类的grade，大于外来类的grade，则返回1（真），则保持他们的相对位置。

显而易见，在排序后为降序数组。

Main函数

internal class Program
    {
           static void Main(string[] args)
           {
           Student[] students = new Student[5];
           students[0] = new Student(50.0, "windows程序设计", "001");
           students[1] = new Student(90.0, "windows程序设计", "002");
           students[2] = new Student(100.0, "windows程序设计", "003");
           students[3] = new Student(70.0, "windows程序设计", "004");
           students[4] = new Student(80.0, "windows程序设计", "005");
           Array.Sort(students);
           foreach (Student student in students) { 
                    Console.WriteLine(student.mygrade);
           };
           Console.Read();
           }
        }
    }

说明：创建了五个学生对象，并且使用sort函数对其grade升序排序。然后依次输出他们排序后的分数。

全部代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace 比较器
{
    public class Student : IComparable
    {
        public double mygrade;
        public string mysubject, myID;
        public Student() { }
        public Student(double grade, string subject, string id)
        {
            mygrade = grade;
            mysubject = subject;
            myID = id;
        }
        int IComparable.CompareTo(Object obj)
        {
            if (obj is Student)
            {
                Student stu = (Student)obj;
                if (this.mygrade > stu.mygrade) { return -1; }
                else if (this.mygrade < stu.mygrade) { return 1; }
                else { return 0; }
            }
            throw new ArgumentException("object is not a Student");
        }
    internal class Program
    {
           static void Main(string[] args)
           {
           Student[] students = new Student[5];
           students[0] = new Student(50.0, "windows程序设计", "001");
           students[1] = new Student(90.0, "windows程序设计", "002");
           students[2] = new Student(100.0, "windows程序设计", "003");
           students[3] = new Student(70.0, "windows程序设计", "004");
           students[4] = new Student(80.0, "windows程序设计", "005");
           Array.Sort(students);
           foreach (Student student in students) { 
                    Console.WriteLine(student.mygrade);
           };
           Console.Read();
           }
        }
    }
}

结果展示：

 总结：

学会了使用比较器对类数组的一个值进行升序，或者降序排序。提供了一个外部比较器.