BNDN F2013: Software Development in Large Teams with International Collaboration C# Quiz

Transcription

1 1 IT University of Copenhagen

2 Outle 1 2.sln) Type Inference 8 Extensions 9 Anonymous Objects 2 IT University of Copenhagen

3 Why a Have a little fun with C# Be a little prepared for F# later this week. We also want to be able to expla how LINQ works. The basics can be hard to comprehend (delegates, lamda s, extension methods, type ference, anonymous objects, function types,...). There are 1000 details about C# - not important here - we can always pose questions about C# that we can t answer - that way C# is not the most beautiful language ever created. 3 IT University of Copenhagen

4 A memorized quote from Anders Hejlsberg at the IT University 2007: C# will keep growg some day it may collapse under its own weight. 4 IT University of Copenhagen

5 .sln) Q1 The variable f.x below represents a: an object of a class b: an stance method c: an stance variable d: none of the above class Foo { t x = 100; class Ma { public static void Ma() { Foo f = new Foo(); Console.WriteLe(f.x); 5 IT University of Copenhagen

6 .sln) Q2 The statement below a: creates a Button control b: itializes a button control c: stantiates button control Choose all that is true private Button dosave = new Button(); 6 IT University of Copenhagen

7 .sln) Q3 What is true about a Constructor? a: it is used to create stantiate objects b: it must have the same name as the class it is declared with c: it maybe overloaded d: a constructor a possible base class is always called e: a, b c f: all of the above 7 IT University of Copenhagen

8 .sln) Q4 Does the program below compile? a: Yes b: No public class Top { public Top(t i) { Console.WriteLe("Top " + i); public class Buttom : Top { public Buttom() { Console.WriteLe("Buttom"); class Program { static void Ma(strg[] args) { Buttom b = new Buttom(); 8 IT University of Copenhagen

9 .sln) Q5 A delegate defes a: a concept of passg methods as first class values b: a class that encapsulates methods c: a means of passg collections to methods d: a governmental representative Choose all that is true above. 9 IT University of Copenhagen

10 .sln) Q6 Polymorphism occurs when a method a child class a: override a method the parent class by extendg the parameter list but matas the same return type. b: mata the same method signature as the method the parent class - however the implementation differs. c: override a method the parent class by matag the same parameter list but changes the return type. d: a c 10 IT University of Copenhagen

11 .sln) Q7 Method Hidg - what is the output? a: A.foo B.foo A.foo b: A.foo B.foo B.foo The compiler gives a warng - why? How to avoid the warng mata the same semantics? public class A { public void foo() { Console.WriteLe("A.foo"); public class B : A { public void foo() { Console.WriteLe("B.foo"); class Program { static void Ma(strg[] args) { A a = new A(); B b = new B(); a.foo(); b.foo(); ((A)b).foo(); 11 IT University of Copenhagen

12 .sln) Same as before without warng from the compiler. public class A { public void foo() { Console.WriteLe("A.foo"); public class B : A { public /**/new/**/ void foo() { Console.WriteLe("B.foo"); class Program { static void Ma(strg[] args) { A a = new A(); B b = new B(); a.foo(); b.foo(); ((A)b).foo(); 12 IT University of Copenhagen

13 .sln) Q8 Method Overridg - what is the output? a: A.foo B.foo A.foo b: A.foo B.foo B.foo This is what we normally expect also know from Java. When you put objects of different herited types to a collection apply a method on each of them, then Hidg Overridg makes a huge difference - is also confusg. public class A { public /**/virtual/**/ void foo() { Console.WriteLe("A.foo"); public class B : A { public /**/override/**/ void foo() { Console.WriteLe("B.foo"); class Program { static void Ma(strg[] args) { A a = new A(); B b = new B(); a.foo(); b.foo(); ((A)b).foo(); 13 IT University of Copenhagen

14 .sln) Q9 About abstract classes methods. Does the program below compile? a: Yes b: No public abstract class AbstractTop { public abstract t foo(t i); public t foo2(t i) { Console.WriteLe("foo2: " + i); return i; public class NotAbstractTop : AbstractTop { public t foo(t i) { Console.WriteLe("foo: " + i); return i; 14 IT University of Copenhagen

15 .sln) Q10 Can a sealed class be a base class? a: Yes b: No Q11 What is true about an abstract class? a: may conta constructors b: may conta implemented methods c: may extend other classes d: may conta stance variables e: a b c f: all of above 15 IT University of Copenhagen

16 .sln) Q12 Say you are codg a threaded GUI application based on Wdows Forms. Can you safely update the value of a GUI control outside the ma GUI thread? a: Yes b: No Q13 What is true about terfaces C# a: an terface can herit from another terface b: an terface can herit from many terfaces c: a class can implement one terface d: a class can implement many terfaces Choose all that apply 16 IT University of Copenhagen

17 Q14 For the code below to compile run the mimum requirements to xs are: a: xs implements IEnumerable b: xs implements IEnumerator c: xs implements both foreach (var i xs) Console.WriteLe(i); 17 IT University of Copenhagen

18 Q15 What is common to the followg collections: System.Collection.ArrayList, System.Collection.HashTable, System.Collection.Queue, System.Collection.SortedList, System.Collection.Stack? a: They get the best out of polymorphism, type safety performance. b: No - polymorphism is obtaed with almost no type safety lots of efficient boxg un-boxg at runtime. 18 IT University of Copenhagen

19 Q16 Does the nonsense to the right compile? a: Yes b: No public terface IA { void fooa(); public terface IB { void foob(); public class MyGeneric<T> where T : IA, IB { T x; public MyGeneric(T x) {this.x = x; public void pp() { this.x.fooa(); this.x.foob(); public class AB : IA { public void fooa() {Console.WriteLe("fooA"); public void foob() {Console.WriteLe("fooB"); class Program { static void Ma(strg[] args) { AB ab = new AB(); var abint = new MyGeneric<AB>(ab); abint.pp(); 19 IT University of Copenhagen

20 Q17 What is written on the console? Q18 Can ListUtil be used on List with elements of any type? public static class ListUtil<T> { public static List<T> map(func<t, T> fn, List<T> xs) { List<T> map2 = new List<T>(); foreach (T x xs) map2.add(fn(x)); return map2; public static void apply(system.action<t> fn, List<T> xs) { foreach (T x xs) fn(x); return; var tlist = new List<t>(new[] {1,2,3,4); var tlist2 = ListUtil<t>.map((x) => x+3,tlist); var tlist3 = ListUtil<t>.map((x) => x*2,tlist2); ListUtil<t>.apply((x) => Console.WriteLe(x), tlist3); 20 IT University of Copenhagen

21 Q19 What is true about dexers? a: You can dex on teger values b: You can dex on strg teger values c: You can overload dexers d: You can have multidimensional dexers e: You can dex on other values than strg tegers Choose all that is true. Q20 What is true about operator overloadg? a: Overloadg works for unary operators b: Overloadg works for bary operators Choose all that is true. 21 IT University of Copenhagen

22 Type Inference Q21 What is true about type ference? a: type ference works for foreach b: type ference works method parameters c: type ference works for return types d: local variable declarations e: type ference works for const declarations f: type ference works for class fields Choose all that is true. Q22 What is valid C# code below? a: (t x) => x % 2==0 b: x => x % 2==0 c: var f = x => x* Choose all that is true. 22 IT University of Copenhagen

23 Type Inference Q23 What is the type of the anonymous method: a: Action<t> b: Func<t,t> c: Action<t,t> Q24 What is the type of the anonymous method: a: Action<t> b: Func<t,t> c: Action<t,t> x => x * x => Console.Write(x*2) 23 IT University of Copenhagen

24 Extensions Q25 What is true about Extensions? a: Extensions to classes are defed non static classes b: Extensions to classes are defed static classes c: Extensions to non static classes must be defed non static. d: Extensions to static classes must be defed static. e: Extensions can be overloaded Choose all that is true. Q26 How can you see that the code below is an extension method to what type how many arguments does the method Prt take? static class BoolExtensions { public static Strg Prt(this bool b) { return(b? "ja" : "nej"); 24 IT University of Copenhagen

25 Extensions Q27 Does Extensions work on terfaces? a) b) a: Yes b: No The answer is crucial for LINQ 25 IT University of Copenhagen

26 Anonymous Objects Q28 Look at the code below. What is true? a: It will compile? b: If it will not compile, then why? c: Can the type of p1 be expressed C#? d: Can p1 p2 be compared? e: Does the order of fields matter when comparg p1 p2? Choose all that is true - if b) is true then assume the malicious statement is removed from the program. var p1 = new { x = 1, y = "foo", z = 3.14 ; p1.x = 42; var p2 = new { x = 42, y = "foo", z = 3.14 ; Console.WriteLe("p1 = p2 : " + (p1 == p2)); 26 IT University of Copenhagen