問題描述
1、使用委託、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）定義一個委託如下 ：
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，方法聲明爲：[6分]
static List<Employee> FindEmployee(Employee[] emps, EmployeePredicate t)（3）寫一個靜態方法FilterBySalary，使之符合委託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的員工找出來並打印。[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後”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後員工找出來並打印。[5分]
（7）利用LINQ技術，把80後員工找出來，按工資從高到低排序，並打印。[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複寫。)[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)），它獨立於要比較的類，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爲0時按Salary進行比較，爲1時按Name排序，爲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、使用委託、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）定義一個委託如下 ：
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，方法聲明爲：[6分]
static List<Employee> FindEmployee(Employee[] emps, EmployeePredicate t)
（3）寫一個靜態方法FilterBySalary，使之符合委託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的員工找出來並打印。[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後”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後員工找出來並打印。[5分]
（7）利用LINQ技術，把80後員工找出來，按工資從高到低排序，並打印。[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複寫。)[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)），它獨立於要比較的類，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爲0時按Salary進行比較，爲1時按Name排序，爲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 employees
where emp.Birthday.IsEighties() == true
orderby emp.Salary descending
select 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 employees
where emp.Birthday.IsEighties() == true
orderby emp.Salary descending
select 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);
}
}
}
運行結果
