Chương 6: Array, Collection Types, and Iterators pptx

Hoang Anh Viet VietHA@it-hut.edu.vn HaNoi University of Technology Chapter 6. Arrays, Collection Types, and Iterators 1 Microsoft 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.” 22 Microsoft 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 3 Microsoft 6.1. Introduction to Arrays  Overview  Implicitly Typed Arrays  Type Convertibility and Covariance  Arrays As Parameters (and Return Values)  The System.Array Base Class 4 Microsoft 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 the memory for the array is allocated on the managed heap.  Array Initialization Syntax:  Example: 100 200 300 myInts[0] myInts[1] myInts[2] Position number of the element within array myInts static void SimpleArrays() { Console.WriteLine("=> Simple Array Creation."); // Create and fill an array of 3 Integers int[] myInts = new int[3]; myInts[0] = 100; myInts[1] = 200; myInts[2] = 300; // Now print each value. foreach(int i in myInts) Console.WriteLine(i); Console.WriteLine(); } 5 Microsoft Figure 6-1: Array of reference types versus value types 6 Microsoft Implicitly Typed Arrays  C# 3.0 introduces an abbreviated way of initializing arrays when the type of the array can be inferred at runtime  When the compiler is presented with multiple types within the initialization list of an implicitly typed array, it determines a type that all the given types are implicitly convertible to.  Example: using System; public class EntryPoint { static void Main() { // A conventional array int[] conventionalArray = new int[] { 1, 2, 3 }; // An implicitly typed array var implicitlyTypedArray = new [] { 4, 5, 6 }; Console.WriteLine( implicitlyTypedArray.GetType() ); // An array of doubles var someNumbers = new [] { 3.1415, 1, 6 }; Console.WriteLine( someNumbers.GetType() ); // Won’t compile! // var someStrings = new [] { "int", // someNumbers.GetType() }; } } 7 Microsoft Type Convertibility and Covariance  When declaring an array to contain instances of a certain type, the instances that may place in that array can actually be instances of a more derived type.  Arrays are covariant  Example: using System; public class Animal { } public class Dog : Animal { } public class Cat : Animal { } public class EntryPoint { static void Main() { Dog[] dogs = new Dog[3]; Cat[] cats = new Cat[2]; Animal[] animals = dogs; Animal[] moreAnimals = cats; } } Dog and Cat are type-convertible to Animal 8 Microsoft Arrays As Parameters (and Return Values)  Once you have created an array, you are free to pass it as a parameter and receive it as a member return value static void PrintArray(int[] myInts) { for(int i = 0; i < myInts.Length; i++) Console.WriteLine("Item {0} is {1}", i, myInts[i]); } static string[] GetStringArray() { string[] theStrings = { "Hello", "from", "GetStringArray" }; return theStrings; } static void PassAndReceiveArrays() { Console.WriteLine("=>Arrays as params and return values."); . int[] ages = {20, 22, 23, 0} ; PrintArray(ages); string[] strs = GetStringArray(); foreach(string s in strs) Console.WriteLine(s); Console.WriteLine(); } Pass array as parameter Get array as return value. 9 Microsoft 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: 10 [...]... 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. .. 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 6.4 Collection Types(2)  The Interface of the System.Collections Namespace  The Class Types of System.Collections  The Sytem.Collections.Generic Namespace Microsoft 21 The Interface of the System.Collections Namespace  The System.Collections... Microsoft public interface ICollection : IEnumerable { int Count { get; } bool IsSynchronized { get; } object SyncRoot { get; } void CopyTo(Array array, int index); } 24 The Role of IDictionary    A dictionary is a collection that maintains a set of name/value pairs Defines a Keys and Values property and Add(), Remove(), Contains() methods public interface IDictionary : ICollection, IEnumerable Definition:... array"); // and print them for (int i = 0; i . Viet VietHA@it-hut.edu.vn HaNoi University of Technology Chapter 6. Arrays, Collection Types, and Iterators 1 Microsoft Objectives “This chapter covers the various array and collection types available in C#. You can create. Arrays  6.4. Collection Types  6.5. Iterators  6.6. Collection Initializers 19 Microsoft 6.4. Collection Types  Ever since its inception, the .NET Framework has offered a host of collection. Arrays  6.4. Collection Types  6.5. Iterators  6.6. Collection Initializers 3 Microsoft 6.1. Introduction to Arrays  Overview  Implicitly Typed Arrays  Type Convertibility and Covariance  Arrays