問題描述

1、使用委托、Lambda表達式、LINQ等知識完成以下內容：(本題35分)

（1）要求定義Employee類，帶有Name屬性（string類型），帶有Birthday屬性（DateTime類型），帶有Salary屬性（double類型）；重載ToString()方法，將信息以適當格式輸出。[8分]

（2）定義一個委托如下 ：

delegate bool EmployeePredicate(Employee emp);

寫一個靜態方法FindEmployee，根據filter參數在數組中查找符合條件的Person實例，方法聲明為：[6分]

static List<Employee> FindEmployee(Employee[] emps, EmployeePredicate t)

（3）寫一個靜態方法FilterBySalary，使之符合委托EmployeePredicate定義，當Salary超過7000時返回true。[3分]

（4）在主方法中添加代碼，結合（2）和（3），將工資超過7000的員工找出來并打印。[3分]

（5）編寫一個靜態類MyExtensions，其中有一個靜態方法Eighties，擴展DateTime類型的功能。如日期符合“80后”定義則返回true，否則返回false。其中年份數據可通過 DateTime的Year屬性訪問到。[5分]

private static bool IsEighties(DateTime dt)

（6）利用（5）中擴展方法寫一個lambda表達式，調用（2）中方法，把80后員工找出來并打印。[5分]

（7）利用LINQ技術，把80后員工找出來，按工資從高到低排序，并打印。[5分]

主方法中已提供以下代碼和數據：

public static void Main(string[] argv){Employee[] employees = new Employee[] {new Employee { Name = "Damon", Birthday = new DateTime(1988, 5, 1), Salary = 4000 },new Employee { Name = "Niki", Birthday = new DateTime(1995, 10, 4), Salary = 7500 },new Employee { Name= "Ayrton", Birthday = new DateTime(1982, 6, 23), Salary = 9200 },new Employee { Name= "Graham", Birthday = new DateTime(1994, 9, 15), Salary = 6800 }};}

2、Array類的靜態Sort方法要求數組中的元素是可比較的。[16分]

1）擴展第1題中Employee類的功能，使之實現泛型IComparable<T>接口（其中定義了方法int CompareTo(T p)），按Salary進行比較。(第1題中已答出的代碼不需要重復寫。)[4分]

2）如果需要以其它方式對Employee對象進行排序，就需要自己創建一個類EmployeeComparer，實現泛型IComparer<T>接口（其中定義了方法int Compare(T a, T b)），它獨立于要比較的類，因此需要兩個參數進行比較。

寫個一EmployeeComparer類，繼承IComparer<T>，內部包含一個整型Sort屬性。當Sort為0時按Salary進行比較，為1時按Name排序，為2時按DateTime排序。其中string類和DateTime類均已實現IComparable接口。[8分]

3）在主方法中實現按Salary和Name的兩種排序。[4分]

解決方案

using System; using System.Collections.Generic; using System.Linq;namespace Homework20 {/**1、使用委托、Lambda表達式、LINQ等知識完成以下內容：(本題35分)（1）要求定義Employee類，帶有Name屬性（string類型），帶有Birthday屬性（DateTime類型），帶有Salary屬性（double類型）；重載ToString()方法，將信息以適當格式輸出。[8分]（2）定義一個委托如下 ：delegate bool EmployeePredicate(Employee emp);寫一個靜態方法FindEmployee，根據filter參數在數組中查找符合條件的Person實例，方法聲明為：[6分]static List<Employee> FindEmployee(Employee[] emps, EmployeePredicate t)（3）寫一個靜態方法FilterBySalary，使之符合委托EmployeePredicate定義，當Salary超過7000時返回true。[3分]（4）在主方法中添加代碼，結合（2）和（3），將工資超過7000的員工找出來并打印。[3分]（5）編寫一個靜態類MyExtensions，其中有一個靜態方法Eighties，擴展DateTime類型的功能。如日期符合“80后”定義則返回true，否則返回false。其中年份數據可通過 DateTime的Year屬性訪問到。[5分]private static bool IsEighties(DateTime dt)（6）利用（5）中擴展方法寫一個lambda表達式，調用（2）中方法，把80后員工找出來并打印。[5分]（7）利用LINQ技術，把80后員工找出來，按工資從高到低排序，并打印。[5分]主方法中已提供以下代碼和數據：public static void Main(string[] argv){Employee[] employees = new Employee[] {new Employee { Name = "Damon", Birthday = new DateTime(1988, 5, 1), Salary = 4000 },new Employee { Name = "Niki", Birthday = new DateTime(1995, 10, 4), Salary = 7500 },new Employee { Name= "Ayrton", Birthday = new DateTime(1982, 6, 23), Salary = 9200 },new Employee { Name= "Graham", Birthday = new DateTime(1994, 9, 15), Salary = 6800 }};}*//**2、Array類的靜態Sort方法要求數組中的元素是可比較的。[16分]1）擴展第1題中Employee類的功能，使之實現泛型IComparable<T>接口（其中定義了方法int CompareTo(T p)），按Salary進行比較。(第1題中已答出的代碼不需要重復寫。)[4分]2）如果需要以其它方式對Employee對象進行排序，就需要自己創建一個類EmployeeComparer，實現泛型IComparer<T>接口（其中定義了方法int Compare(T a, T b)），它獨立于要比較的類，因此需要兩個參數進行比較。寫個一EmployeeComparer類，繼承IComparer<T>，內部包含一個整型Sort屬性。當Sort為0時按Salary進行比較，為1時按Name排序，為2時按DateTime排序。其中string類和DateTime類均已實現IComparable接口。[8分]3）在主方法中實現按Salary和Name的兩種排序。[4分]*/class Employee : IComparable<Employee>{public string Name;public DateTime Birthday;public double Salary;public override string ToString(){return string.Format("{0}: Salary={1}, Birthday={2}", Name, Salary, Birthday);}public int CompareTo(Employee emp){return (int)(Salary - emp.Salary);}}public static class MyExtensions{public static bool IsEighties(this DateTime d){return d.Year > 1979 && d.Year < 1990;}}class EmployeeComparer : IComparer<Employee>{public int Sort { get; set; }public EmployeeComparer(int sort){Sort = sort;}public int Compare(Employee e1, Employee e2){switch (Sort){case 0:return (int)(e1.Salary - e1.Salary);case 1:return e1.Name.CompareTo(e2.Name);default:return e1.Birthday.CompareTo(e2.Birthday);}}}class Program{delegate bool EmployeePredicate(Employee emp);static List<Employee> FindEmployee(Employee[] emps, EmployeePredicate t) {List<Employee> results = new List<Employee>();foreach (Employee p in emps){if (t(p))results.Add(p);}return results;}private static bool FilterBySalary(Employee emp) {return emp.Salary > 7000;}public static void Main(string[] args){Employee[] employees = new Employee[] {new Employee { Name = "Damon", Birthday = new DateTime(1988, 5, 1), Salary = 4000 },new Employee { Name = "Niki", Birthday = new DateTime(1995, 10, 4), Salary = 7500 },new Employee { Name= "Ayrton", Birthday = new DateTime(1982, 6, 23), Salary = 9200 },new Employee { Name= "Graham", Birthday = new DateTime(1994, 9, 15), Salary = 6800 }};List<Employee> high = FindEmployee(employees, FilterBySalary);foreach (Employee emp in high)Console.WriteLine(emp);List<Employee> eighties = FindEmployee(employees, p => p.Birthday.IsEighties());foreach (Employee emp in eighties)Console.WriteLine(emp);var eighties2 = from emp in employeeswhere emp.Birthday.IsEighties() == trueorderby emp.Salary descendingselect emp;foreach (Employee emp in eighties2)Console.WriteLine(emp);Array.Sort(employees);foreach (Employee emp in employees)Console.WriteLine(emp);Array.Sort(employees,new EmployeeComparer(1));foreach (Employee emp in employees)Console.WriteLine(emp);Console.WriteLine("Hello World!");}} }

參考答案

//1、 //(1)class Employee{public string Name { get; set; }public DateTime Birthday { get; set; }public double Salary { get; set; }public override string ToString(){return string.Format("{0}: Salary={1}, Birthday={2}", Name, Salary, Birthday);}} //(2)private static List<Employee> FindEmployee(Employee[] ps, EmployeePredicate t){List<Employee> results = new List<Employee>();foreach (Employee p in ps){if (t(p))results.Add(p);}return results;} //(3)private static bool FilterBySalary(Employee emp){return emp.Salary >= 7000;} //(4)List<Employee> high = FindEmployee(employees, FilterBySalary);foreach(Employee emp in high)Console.WriteLine(emp); //(5)public static class MyExtensions{public static bool IsEighties(this DateTime d){return d.Year > 1979 && d.Year < 1980;}} //(6)List<Employee> eighties = FindEmployee(employees, p => p.Birthday.IsEighties());foreach(Employee emp in eighties)Console.WriteLine(emp); //(7)var eighties2 = from emp in employeeswhere emp.Birthday.IsEighties() == trueorderby emp.Salary descendingselect emp;foreach (Employee emp in eighties2)Console.WriteLine(emp); //2、class Employee : IComparable<Employee>{public string Name { get; set; }public DateTime Birthday { get; set; }public double Salary { get; set; }public override string ToString(){return string.Format("{0}: Salary={1}, Birthday={2}", Name, Salary, Birthday);}public int CompareTo(Employee emp){return (int)(Salary - emp.Salary);}}class EmployeeComparer : IComparer<Employee>{public int Sort { get; set; }public EmployeeComparer(int sort){Sort = sort;}public int Compare(Employee e1, Employee e2){switch(Sort){case 0:return (int)(e1.Salary - e1.Salary);case 1:return e1.Name.CompareTo(e2.Name);default:return e1.Birthday.CompareTo(e2.Birthday);}}}

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運行結果?

參考文章

https://www.cnblogs.com/skm-blog/p/4229487.html

https://www.cnblogs.com/forever-Ys/p/10315830.html

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