Computing is about Data Processing (or "number crunching") Object Oriented Programming is about Cooperating Objects

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2 Computing is about Data Processing (or "number crunching") Object Oriented Programming is about Cooperating Objects C# is fully object-oriented: Everything is an Object: Simple Types, User-Defined Types, even Methods (c)schmiedecke 13 C#-3-Data and Objects 2

3 int, double, char, bool byte, sbyte, short, ushort, uint, long, ulong float, decimal string are Objects shorthand-aliases for System Types System.Int32, System.Double, System.Char... All are.net-types, i.e. common to all.net languages int a = 100; int b = new System.Int32(100); (c)schmiedecke 13 C#-3-Data and Objects 3

4 //Simple Types are.net System Types int mynumber mm System.Int32 mysecondnumber = 12; if (mysecondnumber is int) smile();// identical Type if (mynumber is Int32) smile(); // identical Type //All expected implicit numerical Conversions int a = 1234; decimal b = a; //Explicit numerical conversions //possible loss of information const double PI = 3.141; readonly int truncatedpi = (int)pi; // only 3 (c)schmiedecke 13 C#-3-Data and Objects 4

5 Static class System.Convert does it almost always overflow-checked Names of.net Types Convert.ToBoolean(val) Convert.ToByte(val) Convert.ToChar(val) Convert.ToDecimal(val) Convert.ToInt32(val) Convert.ToString(val)... //val can be any type that "works" exception, if value does not fit (c)schmiedecke 13 C#-3-Data and Objects 5

6 class Names { string firstname; string surname; public Names(string firstname, string surname) { public static implicit operator Name(Names names) { return new Name(names.surname + ", "+names.firstname); class Name { string Name; public Name(string name) { this.name = name; public static explicit operator Names(Name name) { string[] words = name.split(','); return new Name(words[1], words[0]); Names mynames = new Names("Ilse", "Schmiedecke"); Name myname = names; // implicit conversion Names reconstructed = (Names)myName; // explicit conversion (c)schmiedecke 13 C#-3-Data and Objects 6

7 Simple Types own operators +(a,b) identical to a+b Operators are like global static methods Operators can be user-defined through overloading: public static bool operator+ (MyType x, MyType y) { return Combine (x, y); Operators are functions, i.e. they must return a value (c)schmiedecke 13 C#-3-Data and Objects 7

8 It is sometimes useful to add an amout of time to a given time: The trip takes me 3 hours 40, it is now 12:25. When will i arrive? Write an overloaded + operator to your Time class and test it! public static Time operator+ (Time now, Time duration) {... Do the same for the - operator : I need to be there at..., when must i leave? (c)schmiedecke 13 C#-3-Data and Objects 8

9 Simple Types are Value Types Class Instances are Reference Types a: c: 100 int a = 100; Cloud c = new Cloud(); But Simple Types are objects, too? (c)schmiedecke 13 C#-3-Data and Objects 9

10 Class instances are "operating" objects, need an independant lifecycle Simple type "data" are stored and passed by operating objects, lifespan should depend on them. Data Structures are like "big" Simple Types Enumerations are like integers In C#, Enumerations and Structs are Value Types (c)schmiedecke 13 C#-3-Data and Objects 10

11 Structs encapsulate data types like classes no "default" constructor simply declare a variable! custom constructors possible (for initialization) no type hierarchy Contain just like classes: Fields (static and instance), Properties Methods Delegates Indexer (c)schmiedecke 13 C#-3-Data and Objects 11

12 Use Struct without constructor struct Car { int Power; string Type; int YearOfProduction; int age { get {return CurrentYear-YearOfProduction; Car mynewcar; // no constructor needed mynewcar.power = 25; mynewcar.type = "Trabant"; (c)schmiedecke 13 C#-3-Data and Objects 12

13 Class object with own lifecycle, stored on heap inheritance and polymorphism new (constructor call) required for object construction Stuct: Data Structure, stored directly in a variable Lifecycle depends on the variable no inheritance, no polmorphism no parameterless constructor; construction by declaration, "new" optional for initialization (c)schmiedecke 13 C#-3-Data and Objects 13

14 struct Car { int Power; string Type; int YearOfProduction; int age { get {return CurrentYear-YearOfProduction; public void method() { Car mynewcar; mynewcar.power = 25; mynewcar.type = "Trabant"; // mynewcar is lost! public void method(car paramcar) { paramcar.power = 25; paramcar.type = "Trabant"; // paramcar is lost! (c)schmiedecke 13 C#-3-Data and Objects 14

15 Class Limousine{ int Power; string Type; int YearOfProduction; int age { get {return CurrentYear-YearOfProduction; public void method() { Limousine mynewcar; mynewcar.power = 25; mynewcar.type = "Trabant"; // mynewcar is lost! public void method(limousine paramcar) { paramcar.power = 25; paramcar.type = "Trabant"; // paramcar is modified and survives! (c)schmiedecke 13 C#-3-Data and Objects 15

16 Reference type objects live as long as they are referenced Value type objects are destroyed when execution leaves the surrounding block. Value parameters are copied into the method method has no effect on them Reference parameters are referred to by the method method can have effect on them class Names { string firstname; string surname; struct Name { string name; static void deleteentries(names names, Name name) { names.firstname = "deleted"; // reference Type deleted names.surname = "deleted"; name.name = "deleted"; // value type only copy deleted (c)schmiedecke 13 C#-3-Data and Objects 16

17 A Struct is a Utility Data Type "Service" to the Program Used for storing and passing information e.g. Point, personaldatasheet, Contract,... important, where created an kept! Classes are Solutions, program units Using data to do work as a team can be derived from each other, implement interfaces... "Global players" e.g. Drawing, Form, Department, Task, Problem, Connection,... (c)schmiedecke 13 C#-3-Data and Objects 17

18 Would it be a good idea to define Time as a Struct? public struct Time { private int hour; private in minute;... (c)schmiedecke 13 C#-3-Data and Objects 18

19 Enumerations are types of small sets of named values Mapped to integers, can be changed to long, short, byte. Explicit mapping is possible arithmetics are allowed (even if "overflowing" the enum!) automatic ToString() and static Parse(Type, string) method public enum Weekday { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday // mapped to 0-6 private enum Day : byte // only 1 byte long { Sun=1, Mon, Tue, Wed, Thu, Fri, Sat // mapped to 1-7 Weekday today = Weekday.Wednesday; if (today > Weekday.Friday) Shout("Weekend!"); (c)schmiedecke 13 C#-3-Data and Objects 19

20 per default, enums are ints different number size possible particularly useful for binary masking i.e. using logical bit operations to set or read a state enum Access: byte {personal=1, group=2, all=4 Access currentaccess = Access.personal Access.group; if ((currentaccess & Access.personal)!= 0) grantaccess(); (c)schmiedecke 13 C#-3-Data and Objects 20

21 Add days of the week to your Date class, using an enum, and modify your output method accordingly: If you are clever, you can even compute the day from the date, or check it on input... but that is optional. Write a string method ToTurkishDate, using another enumeration. public string ToTurkishDate() {... (c)schmiedecke 13 C#-3-Data and Objects 21

22 Collections are sets of data stored under a common name Arrays: Data of identical type stored in a fixed-size area in memory, accessed by indeces. General Collections: Classes for storing varying amounts of data different access strategies different special properties (c)schmiedecke 13 C#-3-Data and Objects 22

23 Arrays contain data of identical type access via numerical index, starting with O overflow and underflow cause exceptions dimensioning as "jagged arrays": type [][][] System.Array provides poperty Length int[][] jagged = new int[3][]; jagged[0] = new int[2]; jagged[0][0] = 1; jagged[0][1] = 2; jagged[1] = new int[1]; jagged[2] = new int[3] { 3, 4, 5 ; for (int i = 0; i < jagged.length; i++) { int[] innerarray = jagged[i]; foreach (int number in innerarray) { Console.Write(number + " "); Console.WriteLine(); (c)schmiedecke 13 C#-3-Data and Objects 23

24 Block arrays are defined as type [,,, ] Length property of class Array applies in total GetLength method gives dimension lengths Block arrays are nicer, but slower then jagged arrays static void Main() { int[,,] threedimensional = new int[3, 5, 4]; threedimensional[0, 0, 0] = 1; threedimensional[0, 1, 0] = 2; threedimensional[0, 2, 0] = 3; threedimensional[0, 3, 0] = 4; threedimensional[0, 4, 0] = 5; threedimensional[1, 1, 1] = 2; threedimensional[2, 2, 2] = 3; threedimensional[2, 2, 3] = 4; for (int z = 0; z < threedimensional.getlength(2); z++) { for (int y = 0; y < threedimensional.getlength(1); y++) { for (int x = 0; x < threedimensional.getlength(0); x++) { Console.Write(threeDimensional[x, y, i]); Console.WriteLine(); //lines of 3 values Console.WriteLine(); // blocks of 5 lines Console.Writeline("Total Length: "+ threedimensional.length); // 60 (c)schmiedecke 13 C#-3-Data and Objects 24

25 Properties pretend to be fields - but are secured Indexers let classes pretend to be arrays: Object can be accessed using square brackets "index" needs not be numerical, though class FakeArray { this string [int index] { get { int choice = index % 3; if (choice == 0) return "cow"; else if (choice == 1) return "dog"; else return "cat"; private set { FakeArray myarray = new FakeArray(); string mystring = myarray[18]; // cow mystring = myarray[2]; // cat myarray[22] = "spider"; // ignored... (c)schmiedecke 13 C#-3-Data and Objects 25

26 string has an indexer you can access individual chars using square brackets We will learn about List-tpye collections they all have indexers so you can access any List object as if it was an array and many more string word = "Mysecretcodeword"; char firstletter = word[0]; (c)schmiedecke 13 C#-3-Data and Objects 26

27 Begin to design the Appointment type and an Organizer according to Assinment 2. Use an Array to (prototypically) store the appointments. (c)schmiedecke 13 C#-3-Data and Objects 27

28 class Class Model IEnumerable + GetEnumerator() : Enumerator ICollection - Count: int + CopyTo() : ICollection IList - IsFixedSize: boolean - IsReadOnly: boolean - this: IList IDictionary - IsFixedäSize: boolean - IsReadOnly: boolean - Keys: ICollection - this: IDictionary - Values: ICollection + Add() : void + Clear() : void + Contains() : boolean + Add() : void + IndexOf() : int + Clear() : void + Insert() : void + Contains() : boolean + Remove() : void + GetEnumerator() : Enumerator (c)schmiedecke 13 + RemoveAt() : void C#-3-Data and + Objects Remove() : void 28

29 Namespace System.Collections IEnumerable foreach loop is applicable ICollection allows copying between Collections IList indexed collections, fixed order Indexes IDictionary associative Collection, mapping keys to Values static void Main() { int[] arr = new int[3]; arr[0] = 2; arr[1] = 3; arr[2] = 5; LinkedList list = new LinkedList(arr); // Copy to List Hashmap map = new Hashmap() hashmap.add("key1", "value1"); ArrayList list2 = new ArrayList(); map.copyto(list2); // Copy to List (c)schmiedecke 13 C#-3-Data and Objects 29

30 Indexers make objects accessable like arrays Declare "this" property (getter and setter) index may be any type, most commonly int overloading possible! class MockArray { private string low = "low", high = "high"; public string this[int index] { get { if (index < 0) throw new IndexOutOfRangeException(); else if index < 10 ) return low; else return high; set { if (index < 0) throw new IndexOutOfRangeException(); else if index < 10 ) low = value; else high = value; MockArray mock = new MockArray(); mock[12] = mock[8]; (c)schmiedecke 13 C#-3-Data and Objects 30

31 Lists are flexible numbered Collections with fixed order of elements Accessable using an Indexer Most important IList-Implementations ArrayList, Linkedlist, Array SortedList Stack, Queue ArrayList list = new ArrayList(); list.add(2); list.add(3); list.add(7); foreach (object prime in list) Console.WriteLine((int)prime); for (int i = 0; i < list.count; i++) Console.WriteLine((int)(list[i])); list.add(13); list.insert(3, 11); // foreach loop // indexer access (c)schmiedecke 13 C#-3-Data and Objects 31

32 IDictionary describes Maps, or associative collections Key-Value-Pairs Hashtable implements IDictionary Hashtable hashtable = new Hashtable(); hashtable.add("area", 1000); hashtable.add("perimeter", 55); hashtable.add("mortgage", 540); hashtable["year of construction"] = 1955; // Indexer if (hashtable.contains("area")) int area = (int)hashtable["area"]; foreach (object key in hashtable.keys) Console.WriteLine(key.ToString + ": " + hashtable[key].tostring()); (c)schmiedecke 13 C#-3-Data and Objects 32

33 class CollectionsGeneric IEnumerable<T> + GetEnumerator() : Enumerator<T> class Class Model IEnumerable + GetEnumerator() : Enumerator ICollection<T> - Count: int - IsReadOnly: boolean + Add() : void + Clear() : void + Contains() : boolean + CopyTo() : ICollection<T> + Remove() : void IList - IsFixedSize: boolean - IsReadOnly: boolean - this: IList + Add() : void + Clear() : void + Contains() : boolean + IndexOf() : int + Insert() : void + Remove() : void + RemoveAt() : void ICollection - Count: int + CopyTo() : ICollection IDictionary - IsFixedäSize: boolean - IsReadOnly: boolean - Keys: ICollection - this: IDictionary - Values: ICollection + Add() : void + Clear() : void + Contains() : boolean + GetEnumerator() : Enumerator + Remove() : void IList<T> IDictionary<T, Key> - this: IList<T> - Keys: ICollection<T> - this: IDictionary<T, Key> + IndexOf() : int - Values: ICollection<T> + Exists() : void + Insert() : void + Add() : void + RemoveAt() : void + ContainsKey() : boolean (c)schmiedecke 13 + TryGetValue() : <T> C#-3-Data and Objects 33

34 Generic Collections result from a review process type safe access thread safe access much better performance Dictionary<string, int> dict = new Dictionary<string, int>(); dict.add("area", 1000); dict.add("perimeter", 55); dict.add("mortgage", 540); dict["year of construction"] = 1955; // Indexer if (dict.containskey("area")) int area = dict["area"]; // no type casting foreach (string key in dict.keys) Console.WriteLine(key + ": " + dict[key]()); (c)schmiedecke 13 C#-3-Data and Objects 34

35 Implementing IEnumerable requires keeping track of cursors etc. Instead, provide an enumerable list to be used by an iterator keyword "yield return" adds entries to an iterator list Compiler builds iterator. void PrintPowerList() { foreach (int value in ComputePower(2, 30)) Console.WriteLine(value); public static IEnumerable<int> ComputePower (int number, int exponent) { int exponentnum = 0; int numberresult = 1; while (exponentnum < exponent) { numberresult *= number; exponentnum++; yield return numberresult; (c)schmiedecke 13 C#-3-Data and Objects 35

36 For your organizer, choose an appropriate collection to collect all entered dates to keep the collection sorted to be able to output all appointments to be able to look for an appointment. (c)schmiedecke 13 C#-3-Data and Objects 36

37 (c)schmiedecke 13 C#-3-Data and Objects 37