Collections in-csharp

COLLECTIONS IN C#

PRESENTATION CONTENT
1. Concepts Recap
2. What is a collection?
3. Types of Collection
4. Example
5. References

LAKSHMI MAREDDY
CIS525, BELLEVUE UNIVERSITY, NE
INSTRUCTOR: PROF. STUTTE

1. CONCEPTS RECAP

Stacks and Heaps
Value and reference
Interfaces

2/10/2013 Lakshmi Mareddy CIS525 Bellevue University NE 2

1.1 STACK AND HEAP MEMORY

TEMPORARY MEMORY

STACK
Stores variable types in address' in memory, these variables in programming
are called local variables and are often stored for short amounts of time while
a function/method block uses them to compute a task.

HEAP Invoke a
Contains method in a
•attributes, heap
•constructors and
•methods of a class / object
Method’s (function’s) variables
etc. are also stored in stack, but
not in heap, and destroyed after
use.

Heap also sits in stack


1.2 VALUE & TYPE

Point myPoint = new Point (0, 0); // a new value-type variable
Form myForm = new Form(); // a new reference-type variable
Test (ref myPoint, ref myForm); // pass myPoint and myForm by reference

void Test (ref Point p, ref Form f)
{
p.X = 100; // This will change myPoint’s position
f.Text = “Hello, World!”; // This will change MyForm’s caption
f = null; // This will nuke the myForm variable!
}


1.2 SYSTEM INTERFACES IN C#

An interface contains only interface ISampleInterface {
the signatures of void SampleMethod();
methods, }
delegates
class ImplementationClass : ISampleInterface
or events. {
// Explicit interface member implementation:
void ISampleInterface.SampleMethod()
The implementation of the
{
methods is done in the class
// Method implementation.
that implements the interface
}
Defining an interface offers a new
dimension of flexibility (Anyone static void Main()
implementing the interface can
change the way the members are {
coded.) while keeping things // Declare an interface instance.
standard so code will still be uniform. ISampleInterface obj = new
This, in turn, provides a guarantee
that the code won't break when new ImplementationClass();
methods are coded against the same // Call the member.
interface. obj.SampleMethod();
}
}


2. WHAT IS A COLLECTION?

Collections are enumerable data Closely related data can be
structures that can be handled more efficiently when
assessed using indexes or grouped together into a
keys. collection.

In plain English, it is a list, with an Instead of writing separate code
index, to access the list. to handle each individual
object, you can use the same
In programming terms, we are code to process all the
looking at an array, which has elements of a collection.
an index, and can be accessed
via the index


2.1 SYSTEM NAMESPACE

Basic Interfaces

iCollection iEnumerator

iList iEnumerable

iDictionary


2.2 ICOLLECTION

System.Collections.Stack
iCollection System.Collections.Queue
System.Collections.BitArray
System.Collections.Specialized.NameValueCollection


2.2.1 QUEUE

using System;
The Queue is a data using System.Collections;
structure that provides
a First-in-First-Out class Test
collection of items of {
the System.Object static void Main()
type. {
Queue queueObject = new Queue();
The Enqueue() method queueObject.Enqueue(“Peter");
is responsible for queueObject.Enqueue(“Tony");
storing items at the rear queueObject.Enqueue(“Ralph");
of the Queue while (queueObject.Count > 0)

The Dequeue() removes Console.WriteLine(queueObject.Dequeue());
them one at a time Console.ReadLine();
from the front of the }
Queue }


2.3 ILIST

iList
System.Array
System.Collections.ArrayList
System.Collections.Specialized.StringCollection

The iList interface represents
collections that only have value.


2.3.1 ARRAYLIST EXAMPLE

The initial capacity of an using System;
ArrayList is 16, which is using System.Collections;
increased once the 17th class Test
item is stored onto it. {
static void Main()
{
This repeated memory int i = 100;
allocation and copying of double d = 20.5;
the items can be quite ArrayList arrayList = new ArrayList();
expensive in some arrayList.Capacity = 2;
situations. arrayList.Add(“Peter");
arrayList.Add(i);
If we explicitly set the arrayList.Add(d);
for (int index = 0; index <arrayList.Count; index++)
initial size, then we can
Console.WriteLine(arrayList[index]);
improve performance. }
}


2.4 IDICTIONARY

iDictionary
System.Collections.SortedList
System.Collections.Hashtable
System.Collections.Specialized.HybridDictionary
System.Collections.Specialized.ListDictionary

The iDictionary interface represents
collections that have name value pairs.

A Lives at #22, Wisteria Lane

Index to another
Code 0 Is color Red
collection
Looks at Address Book List
Obj X
(Home)


2.4.1 EXAMPLE

using System;
using System.Collections; Similar to the
using System.Collections.Specialized; StringCollection class.
class Test
{ StringDictionary class, is a
static void Main() Hashtable that has its
{ keys as strings only.
StringDictionary stringList = newStringDictionary();
stringList.Add("A", “Ralph");
stringList.Add("B",“China"); A Hashtable can contain any
stringList.Add("C","Jini"); object type in its key.
stringList.Add("D",“Evan");
foreach (string str in stringList.Values)
{
Console.WriteLine(str);
}
}
}


2.5 IENUMERATOR

Enumerators only read data in the
collection; they cannot be used to
modify the underlying collection.

Example: C# foreach statement
Counts through a list, but the statement itself cannot
modify anything.

int[] counter = new int[] { 0, 1, 2, 3, 5, 8, 13 };
foreach (int i in counter) { DO SOMETHING}

ACTION AREA
Moves implicitly through the list WHERE CHANGES
HAPPEN


2.6 IENUMERATOR

String names[]=new String[2] {”Rodney”,”Stutte”,”Cass”};
for(IEnumerator e =names.GetEnumerator();
e.MoveNext();
Response.Write(e.Current));

Output:
CURRENT, MOVENEXT, RESET Rodney
Stutte
Cass

Moves explicitly through the list
Via e.MoveNext();


2.7 IENUMERABLE

IEnumerable is a great example of an interface.
IEnumerable defines just one method:GetEnumerator.
This method returns an Enumerator object for a
collection and that lets you step through the collection
with the For ... Each syntax.


3 WHAT TYPE OF COLLECTION?

Sequential List
Index Access
Key/Value or both
Sortable List
Fast Searches
Only String Type


SEQUENTIAL LIST

• Sequential list where the element is typically
discarded after its value is retrieved
• Queue / Queue generic class / FIFO behavior.
• Stack class / Stack generic class / LIFO behavior.
• The LinkedList generic class allows sequential
access either from the head to the tail or from the
tail to the head.


ACCESS BY INDEX

• The ArrayList and StringCollection classes and
the List generic class offer access to their
elements by the zero-based index of the element.
• The Hashtable, SortedList, ListDictionary, and
StringDictionary classes, and the Dictionary
and SortedDictionary generic classes offer
access to their elements by the key of the
element.
• The NameObjectCollectionBase and
NameValueCollection classes, and the
KeyedCollection and SortedList generic classes
offer access to their elements by either the zero-
based index or the key of the element.


ACCESS BY KEY OR VALUE OR BOTH

• One value: Use any of the collections based on
the IList interface or the IList generic interface.
• One key and one value: Use any of the collections
based on the IDictionary interface or the
IDictionary generic interface.
• One value with embedded key: Use the
KeyedCollection generic class.
• One key and multiple values: Use the
NameValueCollection class.


SORTABLE LIST

• The Hashtable class sorts its elements by their hash
codes.
• The SortedList class and the SortedDictionary
and SortedList generic classes sort their elements by
the key, based on implementations of the iComparer
interface and the iComparer generic interface.
• ArrayList provides a Sort method that takes an
IComparer implementation as a parameter. Its
generic counterpart, the List generic class, provides
a Sort method that takes an implementation of the
iComparer generic interface as a parameter.


FAST SEARCHES

• ListDictionary is faster than Hashtable for small
collections (10 items or fewer).

• The SortedDictionary generic class provides
faster lookup than the Dictionary generic class.


COLLECTIONS THAT ACCEPT ONLY STRING

• StringCollection (based on IList) and
StringDictionary (based on IDictionary) are in
the System.Collections.Specialized
namespace.

You can use any of the generic collection classes
in the System.Collections.Generic namespace
as strongly typed string collections by specifying
the String class for their generic type arguments.


4. EXAMPLES

Okay one final example


ONE FINAL EXAMPLE
using System;
Output using System.Collections;

True class Program
{
True static Hashtable GetHashtable()
{
1000 // Create and return new Hashtable.
Hashtable hashtable = new Hashtable();
hashtable.Add("Area", 1000);
hashtable.Add("Perimeter", 55);
hashtable.Add("Mortgage", 540);
return hashtable;
}

static void Main()
{
Hashtable hashtable = GetHashtable();

// See if the Hashtable contains this key.
Console.WriteLine(hashtable.ContainsKey("Perimeter"));

// Test the Contains method. It works the same way.
Console.WriteLine(hashtable.Contains("Area"));

// Get value of Area with indexer.
int value = (int)hashtable["Area"];

// Write the value of Area.
Console.WriteLine(value);
}
}


5. REFERENCES

Kanjilal J, Working with collections in C#, retrieved on Dec15, 2010 from
http://aspalliance.com/854

Allen Sam, C# Hashtable Use, Lookups and Examples, retrieved on Dec15, 2010 from
http://dotnetperls.com/hashtable

MSDN, Creating and Manipulating Collections, retrieved on Dec15, 2010 from
http://msdn.microsoft.com/en-us/library/14ek9axh(v=vs.80).aspx

MSDN, IEnumerable Interface, retrieved on Dec15, 2010 from
http://msdn.microsoft.com/en-us/library/14ek9axh(v=vs.80).aspx

Albahari Joseph, C# Concepts: Value vs Reference Types, retrieved on Dec15, 2010
from http://www.albahari.com/valuevsreftypes.aspx


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