基础知识 - .Net 程序设计与运行
1.程序设计，猫大叫一声，所有的老鼠都开始逃跑，主人被惊醒。
要求：
A． 要有联动性，老鼠和主人的行为是被动的。
B． 考虑可扩展性，猫的叫声可能引起其他联动效应。
要点：1. 联动效果，运行代码只要执行Cat.Cryed()方法。2. 对老鼠和主人进行抽象
评分标准: .构造出Cat、Mouse、Master三个类，并能使程序运行
从Mouse和Master中提取抽象联动效应，只要执行Cat.Cryed()就可以使老鼠逃跑，主人惊醒。
参考实现：https://www.cnblogs.com/star8521/p/4977912.html
答：a).先抽象定义分别两个接口IObserver和IObserveSubject
namespace ObserverExample { public interface IObserver { void ObserverAction();//对被观察对象的行为作出反应，这里是指猫叫 } } //需要建立不同的文件 namespace ObserverExample { public interface IObserveSubject { void AddObserver(IObserver observer);//添加所有的观察者，在发生动作时对他们进行通知 } }
b).再分别定义实现这两个接口的类
using System; using System.Collections.Generic; namespace ObserverExample { public class Cat : IObserveSubject { List<IObserver> list; public Cat() { list = new List<IObserver>(); } public void AddObserver(IObserver observer) { list.Add(observer);//实现添加观察着对象的方法 } public void Shout() { Console.WriteLine("猫大叫一声..."); //猫叫了，并通知所有的观察者，作出相应的反应 foreach (var item in list) { item.ObserverAction(); } } } } //需要建立不同的文件 using System; namespace ObserverExample { public class Mouse : IObserver { public Mouse(IObserveSubject os) { os.AddObserver(this);//将当前的观察着对象添加到观察者集合中 } public void ObserverAction() { Console.WriteLine("开始逃跑..."); } } } //需要建立不同的文件 using System; namespace ObserverExample { public class Master : IObserver { public Master(IObserveSubject os) { os.AddObserver(this);//将当前的观察着对象添加到观察者集合中 } public void ObserverAction() { Console.WriteLine("惊醒..."); } } }
c).其它方法调用实现
public static void RunCatShout() { Cat c = new Cat(); Mouse m = new Mouse(c); Master master = new Master(c); c.Shout(); }
2.下面的程序执行结果是什么?
class Person { public int Age { get; set; } void RunAge() { int i1 = 20; int i2 = i1; i1++; Console.WriteLine(i2); Person p1 = new Person(); p1.Age = 20; Person p2 = p1; p1.Age++; Console.WriteLine(p2.Age); } }
答：20、21
3.根据线程安全的相关知识，分析以下代码，当调用test方法时i>10时是否会引起死锁?并简要说明理由。
public void test(int i) { lock (this) { if (i > 10) { i--; test(i); } } }
答：不会发生死锁，（但有一点int是按值传递的，所以每次改变的都只是一个副本，因此不会出现死锁。但如果把int换做一个object，那么死锁会发生）
4.在下面的例子里, 当使用new B()创建B的实例时，产生什么输出?
class A { public A() { PrintFields(); } public virtual void PrintFields() { } } class B : A { int x = 1; int y; public B() { y = -1; } public override void PrintFields() { Console.WriteLine("x={0},y={1}", x, y); } }
答：X=1,Y=0;
1． 父类静态成员和静态初始化块 ，按在代码中出现的顺序依次执行
2． 子类静态成员和静态初始化块 ，按在代码中出现的顺序依次执行
3． 父类实例成员和实例初始化块 ，按在代码中出现的顺序依次执行
4． 父类构造方法
5． 子类实例成员和实例初始化块 ，按在代码中出现的顺序依次执行
6． 子类构造方法
5.请使用C#或者Javascript写出如何判断一个数为奇数还是偶数
答：一般普通版:
private bool IsOdd(int num) { return (num % 2) == 1; }
现在升级版: 通过位运算(与)进行判断
private bool IsOdd(int num) { return (num & 1) == 1; }
|
num = 10 0000 1010 0000 0001 |
num = 7 0000 0111 0000 0001 |
| 0000 0000 | 0000 0001 |
function(){ if(t1.value%2==0){ alert("这是个偶数"); }else alert("这是个奇数"); }
5.用C#实现把一个Array复制到ArrayList里。
Array array = new int[] { 1, 2, 3 }; ArrayList arrayList = new ArrayList(array);
6.怎样在多线程中调用同一对象，前提是该对象每分钟会被某一线程改写一次，改写时，其他线程暂停访问，待改写完后再进行访问。
using System; using System.Threading; namespace MultiThread { public class ThreadExample { ThreadObject threadObj; int loopCount = 200; public ThreadExample() { threadObj = new ThreadObject { ThreadRemainIndex = loopCount, ThreadTime = DateTime.Now }; } /// <summary> /// 10. 怎样在多线程中调用同一对象，前提是该对象每分钟会被某一线程改写一次，改写时，其他线程暂停访问，待改写完后再进行访问。 /// </summary> public void TestMultiThreadReadWrite() { //Thread ParameterizedThreadStart ts_read = new ParameterizedThreadStart(ReadThreadObject); ThreadStart ts_write = new ThreadStart(WriteThreadObject); Thread t1 = new Thread(ts_read); Thread t2 = new Thread(ts_read); Thread t3 = new Thread(ts_write); Thread t4 = new Thread(ts_read); Thread t5 = new Thread(ts_read); Thread t6 = new Thread(ts_read); Thread t7 = new Thread(ts_read); t1.Start("t1"); t2.Start("t2"); t3.Start(); t4.Start("t4"); t5.Start("t5"); t6.Start("t6"); t7.Start("t7"); } private object writeObj = new object(); public void ReadThreadObject(object threadNum) { //lock (writeObj) //{ for (int i = 0; i < loopCount; i++) { lock (writeObj) { if (threadObj.ThreadRemainIndex <= 0) break; Thread.Sleep(100); Console.WriteLine("Read ThreadTime:{0:yyyy-MM-dd HH:MM:ss.fff},ThreadNum:{1}，ThreadRemainIndex:{2}", threadObj.ThreadTime, threadNum, threadObj.ThreadRemainIndex); threadObj.ThreadRemainIndex -= 1; } } //} } public void WriteThreadObject() { //lock (writeObj) //{ for (int i = 0; i < loopCount; i++) { lock (writeObj) { if (threadObj.ThreadRemainIndex <= 0) break; Thread.Sleep(150); threadObj.ThreadTime = DateTime.Now; Console.WriteLine("Write hreadTime:{0:yyyy-MM-dd HH:MM:ss.fff}，ThreadRemainIndex:{1}", threadObj.ThreadTime, threadObj.ThreadRemainIndex); //lock (writeObj) threadObj.ThreadRemainIndex -= 1; } } } } public class ThreadObject { public int ThreadRemainIndex { get; set; } public DateTime ThreadTime { get; set; } } }
using System; using System.Collections.Generic; using System.Threading; using System.Threading.Tasks; namespace MultiThread { public class ThreadObserverExample { ThreadObject threadObj; int loopCount = 200; public ThreadObserverExample() { threadObj = new ThreadObject { ThreadRemainIndex = loopCount, ThreadTime = DateTime.Now }; } public void TestMultiThreadReadWrite() { //因为没有使用锁，所以ThreadRemainIndex会出现负数的情况 Action<object> act_read = (threadNum) => { for (int i = 0; i < loopCount; i++) { if (threadObj.ThreadRemainIndex <= 0) break; Thread.Sleep(100); Console.WriteLine("Read ThreadTime:{0:yyyy-MM-dd HH:MM:ss.fff},ThreadNum:{1}，ThreadRemainIndex:{2}", threadObj.ThreadTime, threadNum, threadObj.ThreadRemainIndex); threadObj.ThreadRemainIndex -= 1; } }; Action act_write = () => { for (int i = 0; i < loopCount; i++) { if (threadObj.ThreadRemainIndex <= 0) break; Thread.Sleep(150); threadObj.ThreadTime = DateTime.Now; Console.WriteLine("Write hreadTime:{0:yyyy-MM-dd HH:MM:ss.fff}，ThreadRemainIndex:{1}", threadObj.ThreadTime, threadObj.ThreadRemainIndex); //lock (writeObj) threadObj.ThreadRemainIndex -= 1; } }; Task t1 = new Task(act_read, "t1"); Task t2 = new Task(act_read, "t2"); Task t3 = new Task(act_read, "t3"); Task t4 = new Task(act_write); Task t5 = new Task(act_read, "t5"); Task t6 = new Task(act_read, "t6"); Task t7 = new Task(act_read, "t7"); ThreadSubject ts = new ThreadSubject(); ts.AddObserver(t1); ts.AddObserver(t2); ts.AddObserver(t3); ts.AddObserver(t5); ts.AddObserver(t6); ts.AddObserver(t7); ts.WriteObject(t4); } public interface IThreadObserveSubject { void AddObserver(Task observer); void WriteObject(Task subject); } public class ThreadSubject : IThreadObserveSubject { List<Task> list; public ThreadSubject() { list = new List<Task>(); } public void AddObserver(Task observer) { list.Add(observer); //observer.Start(); } public void WriteObject(Task subject) { foreach (Task t in list) { if (t.Status == TaskStatus.Running) t.Wait(); else t.Start(); } subject.Start(); if (subject.IsCompleted) { subject.Wait(); foreach (Task t in list) { t.Start(); } } } } } }
7.将List<ClassA> obj 中的所有元素复制给另一个List<ClassA> obj2对象，有几种方法？复制后使用obj2 会出现什么问题？
参考答案：https://www.cnblogs.com/insus/p/8127745.html
答：有区分浅复制/深复制，值类型/引用类型；分别有：List<T> 自带的CopyTo方法，List<T> 自带的GetRange方法，List<T> 的构造方法 List(IEnumerable<T> collection)，序列化与反序列化;
using System; using System.Collections.Generic; using System.IO; using System.Linq; using System.Runtime.Serialization.Formatters.Binary; namespace Helper { static class ListExtensions { public static IList<T> Clone<T>(this IList<T> listToClone) where T : ICloneable { return listToClone.Select(item => (T)item.Clone()).ToList(); } //当然前题是List中的对象要实现ICloneable接口 } public class Question0628 { //11. 将List<ClassA> obj 中的所有元素复制给另一个List<ClassA> obj2对象，有几种方法？复制后使用obj2 会出现什么问题？ public void CopyList() { Func<List<ClassA>, List<ClassA>> copyList = (sourceList) => { List<ClassA> resultList; ClassA[] array = new ClassA[sourceList.Count]; sourceList.CopyTo(array); resultList = array.ToList(); return resultList; }; Action<List<ClassA>, string> act_read = (list, listName) => { Console.WriteLine(listName); foreach (ClassA item in list) { Console.WriteLine("Id:{0},Name:{1}", item.Id, item.Name); } }; List<ClassA> list1 = new List<ClassA> { new ClassA { Id = 1, Name = "C1" }, new ClassA { Id = 2, Name = "C2" }, new ClassA { Id = 3, Name = "C3" } }; act_read(list1, "list1"); Console.WriteLine("copying..."); List<ClassA> list2 = copyList(list1); List<ClassA> list3 = new List<ClassA>(list1); List<ClassA> list4 = list1.Clone().ToList(); List<ClassA> list5 = list1.GetRange(0, list1.Count); List<ClassA> list6; using (MemoryStream ms = new MemoryStream()) { BinaryFormatter bf = new BinaryFormatter(); bf.Serialize(ms, list1); ms.Position = 0; list6 = (List<ClassA>)bf.Deserialize(ms); } //list2 change list2.ForEach(f => f.Name = f.Name + "_" + "list2"); act_read(list1,"list1"); act_read(list2, "list2:"); act_read(list3, "list3:"); act_read(list4, "list4:"); act_read(list5, "list5:"); act_read(list6, "list6:"); } [Serializable] public class ClassA : ICloneable { public int Id { get; set; } public string Name { get; set; } public object Clone() { //自己重写的Clone return new ClassA { Id = Id, Name = Name }; } } } }
8.以下方法被调用时会输出什么？
Public void Printout(){ Var longName=”LawExam”; longName.Replace(“Exam”,”Go”); longName.Insert(3,”-”); Console.WriteLine(longName); }
答：LawExam
9.C#代码中，下列分别输出什么？
int a=1; Console.WriteLine(a is dynamic); int? a = 1; Console.WriteLine(a is int); int? a = 1; Console.WriteLine(a.GetType() == typeof(int?));
答：True，True，False
10.执行以下代码片段输出什么？
Action doit = async () => { Console.WriteLine(1); var task = Task.Run(() => { Thread.Sleep(3000); Console.WriteLine(2); }); await task; Console.WriteLine(3); }; doit();
答：1，2，3
11.How to get all combinations from “allList”? Such as a1A,a1B,....c3E
List<List<string>> allList= new List<List<string>> { new List<string> {“a”,”b”,”c”}, new List<string> {“1”,”2”,”3”}, new List<string> {“A”,”B”,”C” ,”D”,”E”}, };
List<string> outList = new List<string>(); Func<List<string>, List<string>,List<string>> act = (list1, list2) => { List<string> result = new List<string>(); foreach (string str in list1) { list2.ForEach(f => { string str2 = str + f; result.Add(str2); }); } return result; }; foreach (var list in allList) { if (outList.Count == 0) { outList = list; continue; } outList = act(outList, list); } Console.WriteLine(string.Join(",", outList));
12.Write a singleton class of threaded safe.
public class MyFactory { private static class instanceHolder { public static MyFactory instance = new MyFactory(); } public static MyFactory getInstance() { return MyFactory.instanceHolder.instance; } }
13.What is the output of the program below? Explain your answer.
Class program { delegate void Printer(); static void main(string[] args) { List<Printer> printers = new List<Printer>(); for (int i = 0; i < 10; i++) { printers.Add(delegate { Console.WriteLine(i); }); } foreach (var printer in printers) { printer(); } } }
答：10个10，因为所有的委托中的变量i都是指向同一块内存地址
14.What is the output of the program below? Explain your answer.
Class Program { private static string result; static void Main(string[] args) { SaySomething(); Console.WriteLine(result); Console.ReadKey(true); } static async Task<string> SaySomething() { Await Task.Delay(5); result=”Hello world!”; return “Something”; } }
Also,would the answer change if we were to replace await Task.Delay(5) with Thread.Sleep(5)? Why or why not?
答：null，什么也没输出；会改变，Thread.Sleep 是同步延迟，Task.Delay异步延迟。
Thread.Sleep 会阻塞线程，Task.Delay不会。
15.To generate 6 random and unique members between 1 and 49,what way you think fast?
static void func_1() { int nowNum = 0; int[] array = new int[6]; var r = new Random(); while (nowNum < 6) { int v = r.Next(1, 49); bool flag = false; for (int i = 0; i < nowNum; i++) { if (v == array[i]) { flag = true; break; } } if (!flag) array[nowNum++] = v; } Console.WriteLine(string.Join(",", array)); }
16.请编程实现一个冒泡排序算法
static void bubble() { int[] arr = { 23, 44, 66, 76, 98, 11, 3, 9, 7 }; int temp = 0; for (int i = 0; i < arr.Length - 1; i++) { for (int j = 0; j < arr.Length - 1 - i; j++) { if (arr[j] > arr[j + 1]) { temp = arr[j + 1]; arr[j + 1] = arr[j]; arr[j] = temp; } } } string result = string.Join(",", arr); Console.WriteLine(result); }
99.一个完整的软件项目开发过程需要经历哪几个步骤？每个步骤会有哪些成果？
答：一、问题的定义及规划
此阶段是软件开发与需求放共同讨论，主要确定软件的开发目标及其可行性。
【团队/管理评审/背景调查/项目目标/角色/模块接口】
二、需求分析
在确定软件开发可行性的情况下，对软件需要实现的各个功能进行详细需求分析。
【产品原型/业务流程图/项目里程碑】
三、软件设计
软件设计一般分为总体设计和详细设计
【UI设计规范/系统框架设计/数据库设计】
四、程序编码
此阶段是将软件设计的结果转化为计算机可运行的程序代码。在程序编码中必定要制定统一、符合标准的编写规范。以保证程序的可读性、易维护性。提高程序的运行效率。
五、软件测试
编写测试用例，整个测试阶段分为单元测试、流程测试三个阶段进行。
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