Chương 6: Array, Collection Types, and Iterators

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This chapter covers the various array and collection types available in C#. You can create two types of multidimensional arrays, as well as your own collection types while utilizing collection-utility classes.

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Nội dung Text: Chương 6: Array, Collection Types, and Iterators

Chapter 6. Arrays, Collection Types, and Iterators Hoang Anh Viet VietHA@it-hut.edu.vn HaNoi University of Technology 1
Objectives “This chapter covers the various array and collection types available in C#. You can create two types of multidimensional arrays, as well as your own collection types while utilizing collection-utility classes. You’ll see how to define forward, reverse, and bidirectional iterators using the new iterator syntax introduced in C# 2.0, so that your collection types will work well with foreach statements.” Microsoft 2
Roadmap 6.1. Introduction to Arrays  6.2. Multidimentional Rectangular Arrays  6.3. Multidimentional Jagged Arrays  6.4. Collection Types  6.5. Iterators  6.6. Collection Initializers  Microsoft 3
6.1. Introduction to Arrays Overview  Implicitly Typed Arrays  Type Convertibility and Covariance  Arrays As Parameters (and Return Values)  The System.Array Base Class  Microsoft 4
Overview An array is a set of data items, accessed using an numerical index  An array is a group of contiguous memory locations that all have  the same name and type Arrays are reference types, and  static void SimpleArrays() the memory for the array is { allocated on the managed heap. Console.WriteLine("=> Simple Array Creation."); // Create and fill an array of 3 Integers Array Initialization Syntax:  int[] myInts = new int[3]; myInts[0] = 100; Example:  myInts[1] = 200; 100 myInts[0] myInts[2] = 300; // Now print each value. Position number of the element within array myInts foreach(int i in myInts) 200 myInts[1] Console.WriteLine(i); Console.WriteLine(); 300 } myInts[2] Microsoft 5
Figure 6-1: Array of reference types versus value types Microsoft 6
Implicitly Typed Arrays using System; public class EntryPoint C# 3.0 introduces an  { abbreviated way of initializing static void Main() arrays when the type of the { array can be inferred at // A conventional array int[] conventionalArray = new int[] { 1, 2, 3 }; runtime // An implicitly typed array When the compiler is  var implicitlyTypedArray = new [] { 4, 5, 6 }; presented with multiple types Console.WriteLine( implicitlyTypedArray.GetType() ); within the initialization list of an // An array of doubles implicitly typed array, it var someNumbers = new [] { 3.1415, 1, 6 }; Console.WriteLine( someNumbers.GetType() ); determines a type that all the // Won’t compile! given types are implicitly // var someStrings = new [] { "int", convertible to. // someNumbers.GetType() }; Example:  } } Microsoft 7
Type Convertibility and Covariance using System; public class Animal { } When declaring an array to  public class Dog : Animal { } contain instances of a certain public class Cat : Animal { } type, the instances that may public class EntryPoint place in that array can actually Dog and Cat are { type-convertible to be instances of a more derived Animal static void Main() type. { Arrays are covariant  Dog[] dogs = new Dog[3]; Example: Cat[] cats = new Cat[2];  Animal[] animals = dogs; Animal[] moreAnimals = cats; } } Microsoft 8
Arrays As Parameters (and Return Values) static void PrintArray(int[] myInts) { for(int i = 0; i < myInts.Length; i++) Once you have created an Console.WriteLine("Item {0} is {1}", i, myInts[i]);  } array, you are free to pass it as static string[] GetStringArray() a parameter and receive it as a { member return value string[] theStrings = { "Hello", "from", "GetStringArray" }; return theStrings; } static void PassAndReceiveArrays() { Console.WriteLine("=>Arrays as params and return values."); . int[] ages = {20, 22, 23, 0} ; Pass array as parameter PrintArray(ages); string[] strs = GetStringArray(); foreach(string s in strs) Get array as return value. Console.WriteLine(s); Console.WriteLine(); } Microsoft 9
The System.Array Base Class The System.Array type houses the fundamental  methods and properties that are essential to an array Some members:  Clear() : set a range of elements in the array to empty values.  CopyTo() : copy elements from the source array into the  destination array Length : return the number of items  Rank : return the number of dimensions  Reverse() : reverse the contents of a one-dimensional array  Sort() : sort a one-dimensional array fo intrinsic types   Example: Microsoft 10
using System; namespace ConsoleApplication11 { class Program { static void Main() { SystemArrayFunctionality(); Initialize Console.ReadLine(); items at } startup static void SystemArrayFunctionality() { Console.WriteLine("=> Working with System.Array."); . string[] gothicBands = { "Tones on Tail", "Bauhaus", "Sisters of Mercy" }; // Print out names in declared order. Console.WriteLine(" -> Here is the array:"); for (int i = 0; i
Console.WriteLine("\n"); Array.Reverse(gothicBands); Console.WriteLine(" -> The reversed array"); // ... and print them. Reverse for (int i = 0; i
Roadmap 6.1. Introduction to Arrays  6.2. Multidimentional Rectangular Arrays  6.3. Multidimentional Jagged Arrays  6.4. Collection Types  6.5. Iterators  6.6. Collection Initializers  Microsoft 13
6.2. Multidimensional Rectangular Arrays using System; Declaration public class EntryPoint Each row contains the same  { number of columns static void Main() { Explicit Don’t need the size of each  dimension int[,] twoDim1 = new int[5, 3]; dimension when declaring the size int[,] twoDim2 = { {1, 2, 3}, type {4, 5, 6}, When creating an instance of  {7, 8, 9} }; the array type, you must foreach (int i in twoDim2) Figured out provide the size of the base on { dimensions. initialization Console.WriteLine(i); expression Get the count of each  } dimension: Array.GetLength } } Microsoft 14
Roadmap 6.1. Introduction to Arrays  6.2. Multidimentional Rectangular Arrays  6.3. Multidimentional Jagged Arrays  6.4. Collection Types  6.5. Iterators  6.6. Collection Initializers  Microsoft 15
6.3 Multidimensional Jagged Arrays A jagged array is an array of arrays.  Each of the rows need not be the same size as all the  others, a graphical representation of the array would not be square. Create a jagged array:  Declaration Declare the number of rows in array.  Each row will hold an array, which can be of any length.  int[][] jagged = new int[3][]; These arrays must each = new int[] { 1, 2 }; jagged[0] be declared.  Then fill in the values for=the elements 3, 4, 5 }; "inner" arrays. jagged[1] new int[] { 1, 2, in these  Has different size jagged[2] = new int[] { 6, 5, 4 }; foreach (int[] ar in jagged) Microsoft 16
for (int i = 0; i < jagged.Length; ++i) { StringBuilder sb = new StringBuilder(); for (int j = 0; j < jagged[i].Length; ++j) Use for statement { sb.AppendFormat("{0} ", jagged[i][j]); } Console.WriteLine(sb.ToString()); } foreach (int[] ar in jagged) { StringBuilder sb = new StringBuilder(); Use foreach statement foreach (int n in ar) { sb.AppendFormat("{0}", n); } Console.WriteLine(sb.ToString()); } Microsoft 17
using System; 1. using System.Text; 2. public class EntryPoint 3. { 4. static void Main() 5. { 6. int[][] jagged = new int[3][]; 7. jagged[0] = new int[] { 1, 2 }; 8. jagged[1] = new int[] { 1, 2, 3, 4, 5 }; 9. jagged[2] = new int[] { 6, 5, 4 }; 10. foreach (int[] ar in jagged) 11. { 12. StringBuilder sb = new StringBuilder(); 13. foreach (int n in ar) 14. { 15. sb.AppendFormat("{0} ", n); 16. } 17. Console.WriteLine(sb.ToString()); 18. } 19. Console.WriteLine(); 20. for (int i = 0; i < jagged.Length; ++i) 21. { 22. StringBuilder sb = new StringBuilder(); 23. for (int j = 0; j < jagged[i].Length; ++j) 24. { 25. sb.AppendFormat("{0} ", jagged[i][j]); 26. } 27. Console.WriteLine(sb.ToString()); 28. } 29. } 30. } 31. Microsoft 18
Roadmap 6.1. Introduction to Arrays  6.2. Multidimentional Rectangular Arrays  6.3. Multidimentional Jagged Arrays  6.4. Collection Types  6.5. Iterators  6.6. Collection Initializers  Microsoft 19
6.4. Collection Types Ever since its inception, the .NET Framework has  offered a host of collection types for managing everything from an expandable array via ArrayList, a Queue, a Stack, or even a dictionary via the HashTable class. Over the years, newer version of the .NET Framework expanded these types. Generally, a collection is any type that holds on to a set of objects and implements IEnumerable or IEnumerable. The objects in the set are typically related to each other in some way defined by the problem domain. Microsoft 20