Chương 6: Array, Collection Types, and Iterators pptx

You can create two types of multidimensional arrays, as well as your own collection types while utilizing collection-utility classes.. Overview  An array is a set of data items, accesse

Hoang Anh Viet

VietHA@it-hut.edu.vn

HaNoi University of Technology

Chapter 6 Arrays, Collection

Types, and Iterators

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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.”

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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

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6.1 Introduction to Arrays

 Implicitly Typed Arrays

 Type Convertibility and Covariance

 The System.Array Base Class

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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:

100200300

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];

Console.WriteLine();

}

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Figure 6-1: Array of reference types versus value types

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Implicitly Typed Arrays

abbreviated way of initializing

arrays when the type of the

array can be inferred at

runtime

presented with multiple types

within the initialization list of an

implicitly typed array, it

determines a type that all the

given types are implicitly

// 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() };

} }

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Type Convertibility and Covariance

contain instances of a certain

type, the instances that may

place in that array can actually

be instances of a more derived

type

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

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Arrays As Parameters (and Return

Values)

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;

Pass array as parameter

Get array as return value.

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The System.Array Base Class

properties that are essential to an array

 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

 Reverse() : reverse the contents of a one-dimensional array

 Sort() : sort a one-dimensional array fo intrinsic types

 Example :

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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 <= gothicBands.GetUpperBound(0); i++)

Console.WriteLine( "\n");

Array.Reverse(gothicBands);

Console.WriteLine( " -> The reversed array");

// and print them.

for (int i = 0; i <= gothicBands.GetUpperBound(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

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dimension when declaring the

type

the array type, you must

provide the size of the

Declaration

Explicit dimension size

Figured out base on initialization expression

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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

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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

Has different size

int[][] jagged = new int[3][];

jagged[0] = new int[] { 1, 2 };

jagged[1] = new int[] { 1, 2, 3, 4, 5 };

jagged[2] = new int[] { 6, 5, 4 };

foreach (int[] ar in jagged)

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StringBuilder sb = new StringBuilder();

foreach (int n in ar)

StringBuilder sb = new StringBuilder();

for (int j = 0; j < jagged[i].Length; ++j)

7 int [][] jagged = new int [3][];

8 jagged[0] = new int [] { 1, 2 };

9 jagged[1] = new int [] { 1, 2, 3, 4, 5 };

10 jagged[2] = new int [] { 6, 5, 4 };

11 foreach ( int [] ar in jagged)

12 {

13 StringBuilder sb = new StringBuilder ();

14 foreach ( int n in ar)

23 StringBuilder sb = new StringBuilder ();

24 for ( int j = 0; j < jagged[i].Length; ++j)

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

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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<T> The objects in the set are typically related to each other in some way defined by the problem domain.

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6.4 Collection Types(2)

 The Interface of the System.Collections

Namespace

 The Class Types of System.Collections

 The Sytem.Collections.Generic Namespace

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The Interface of the System.Collections Namespace

 Amajority of the classes within System.Collections implement these interfaces to provide access to their contents

 Allows Containers to automatically resize themselves

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The Role of ICollection

 The number of items in the container

 The thread safety of the container

 The ability to copy the contents into a System.Array type

void CopyTo(Array array, int index);

}

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The Role of IDictionary

Contains() methods.

public interface IDictionary : ICollection, IEnumerable {

bool IsFixedSize { get; } bool IsReadOnly { get; } // Type indexer

object this[object key] { get; set; } ICollection Keys { get; }

ICollection Values { get; } void Add(object key, object value);

The Role of IList

a container

bool IsFixedSize { get; } bool IsReadOnly { get; } object this[ int index ] { get; set; } int Add(object value);

void Clear();

bool Contains(object value);

int IndexOf(object value);

void Insert(int index, object value);

void Remove(object value);

void RemoveAt(int index);

}

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// Public fields for simplicity.

public string PetName;

public int Speed;

static void ArrayListTest()

{

Console.WriteLine( "\n=> ArrayList Test:\n");

ArrayList carArList = new ArrayList();

carArList.AddRange(new Car[] { new Car( "Fred", 90, 10),

new Car( "Mary", 100, 50), new Car( "MB", 190, 11)});

Console.WriteLine( "Items in carArList: {0}", carArList.Count);

// Print out current values.

foreach(Car c in carArList)

Console.WriteLine( "Car pet name: {0}", c.PetName);

Console.WriteLine( "->Inserting new Car.");

carArList.Insert(2, new Car( "TheNewCar", 0, 12));

Console.WriteLine("Items in carArList: {0}", carArList.Count);

object[] arrayOfCars = carArList.ToArray();

for(int i = 0; i < arrayOfCars.Length; i++)

Print out # of items in ArrayList.

Insert a new item.

Get object array from ArrayList

Working with the Queue Type

 Queues are containers that ensure items are accessed using a

first-in, first-out manner

Queue

removing it

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The System.Collections.Generic

Namespace

 Contains numerous class and interface types that allow you to

contain subitems in a variety of containers

 Similar to System.Collections but more general

 Differences:

• TValue : used for values

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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

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6.5 Iterators

 When the enumerable object calls GetEnumerator , either directly or indirectly, the compiler generates and returns an appropriate iterator object

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Enumerable Objects

public interface IEnumerable<T> : IEnumerable {

to enumerate nongeneric

collections

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Enumerators

 Enumerators are part of the enumeration pattern and normally

implemented as a nested class within the collection type

public interface IEnumerator<T> : IEnumerator, IDisposable {

T Current { get; } }

public interface IEnumerator {

object Current { get; } bool MoveNext();

Returns the enumeration

to the beginning of the

collection

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 The enumerator is the state machine representing the enumeration

 Part of the state machine is the cursor, which is the collection index

or locator

 When the enumerator is created, the cursor initially points before the first element of the collection

the Current property to the next element of the collection

 The Reset method resets the enumeration He cursor is updated to point to before the collection again

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elements = new object[items.Length];

Array.Copy(items, elements, items.Length);

throw new InvalidOperationException(

"Enumeration already finished");

}

if (cursor == -1)

{

throw new InvalidOperationException(

"Enumeration not started");

}

return elements[cursor];

}

}

private int cursor;

private object[] elements = null;

}

private object[] items = null;

}

}

IEnumerable<T>, IEnumerator<T>,

IEnumerable, and IEnumerator

 The C# foreach statement iterates over a collection of objects,

including a System.Array, ArrayList, List<T>…which implement the IEnumerable<T> or IEnumerable interface

 These interfaces allow iterating easier and more friendly

 Definitions:

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The statement expression is assigned to the Current property

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Iterator block

 Contains the logic to enumerate a

collection

 Includes one or more yield statements

 Methods,properties, and operator function can be iterator block

 Maintains the state machine of the

enumerator between iterations

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{ Console.WriteLine(n);

} } }

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

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6.6 Collection Initializers

 C# 3.0 introduces a new abbreviated syntax for initializing

collections

 For each item in the collection initialization list, the compiler

generates a call to the collection’s Add() method

 The collection type must implement ICollection<T>

 Each item in the collection initialization list must be implicitly

convertible to the type T

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var developmentTeam = new List<Employee> {

new Employee { Name = "Michael Bolton" },

new Employee { Name = "Samir Nagheenanajar" },

new Employee { Name = "Peter Gibbons" }

};

Console.WriteLine( "Development Team:" );

Summary

 I’ve introduced you about arrays and collections which are very

useful to store values and imply the relations between stored types

 I ‘ve also supplied the use of arraylist and queue and how to

enumerate items with foreach statement

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