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INDEXERS
What’s an indexer?
An array has an indexer…
int[] myArray = new int[5];for (int index = 0; index < 5; ++index){ myArray[index] = 3;}
The [ ] is the indexer.
What’s an indexer?
An indexer accesses one value by using another value
A special property: public <type> this[<index_type> <index_value>]
The index_type is often an integer, but can be another data type
Implemented on collection classes Throws an ArgumentException
ArgumentNullExceptionArgumentOutOfRangeException
Indexer Exampleclass MyThing{}
class MyCollection{ public void AddThing(MyThing inThing) { ... }
public MyThing this[int index] { get { ... } set { ... } }}
DELEGATES AND EVENTS
Start with an Example
What’s a delegate?
A delegate specifes a method signature for an event
A special data type:public delegate <return_type> DelegateName([parameters_list]);
Delegate Example// The delegate type declarationpublic delegate void NameChangedEventHandler(object sender, EventArgs e);
class NameObject{ // The event member public event NameChangedEventHandler NameChanged;
public void setName(string inName) { mName = inName; if (NameChanged != null) { NameChanged(this); } }}
Connecting to an Eventclass SomeObject{ private NameObject mTheName = new NameObject();
public void Init() { mTheName.NameChanged += new NameChangedEventHandler(EventHandler) }
private void EventHandler(object sender) { }}
OPERATOR OVERLOADING
What operations?
Unary operators+, -, !, ++, --, true, falsepublic static <return_type>operator <operator>(<operand_type>)
Binary operators+, -, *, /, %, &, |, ==, !=, >, <, >=, <=public static <return_type>operator <operator>(<operand_type_1>,
<operand_type_2>)
Operator Exampleclass MyCollection{ private List<object> mList;
public static MyCollection operator +(MyCollection col, object newObject)
{ col.mList.Add(newObject); return col; }}
collection += new object();
Overloading ==
Must also overload Equals() Must also overload GetHashCode() Must also overload !=
Must overload relational operators in pairs (<, >), (<=, >=), (==, !=)
Practice Exercise
Exercise 13-1, p. 418
CLASS INHERITANCE
What is inheritance? One class inherits the attributes and
behaviors of another class The base class should be a larger
classification of the derived class (ex. a Control is a larger classification for Button)A Button “is-a” Control; a Button “has-a”
BackColorA Book “is-a” Product; a Book “has-a” Publisher
The derived class extends or overrides behavior
.NET Inheritance
All classes implicitly inherit from System.ObjectGetType()ToString()Equals()ReferenceEquals()GetHashCode()Finalize()MemberwiseClone()
How does inheritance work?
class Fourth class Third class Second class First
methodA
methodB methodB
methodC methodC methodC
methodD methodD
methodE methodE
Fourth fourth = new Fourth();fourth.methodA();fourth.methodB();fourth.methodC();fourth.methodD();fourth.methodE();
First first = new Fourth();first.methodA();first.methodB();first.methodC();first.methodD();first.methodE();
“Polymorphism”The base class can take many different
forms.
Polymorphism
List<First> myList = new List<First>();myList.Add(new First());myList.Add(new Second());myList.Add(new Third());myList.Add(new Fourth());
foreach (First item in myList){ item.methodB(); item.methodC();}
How do we “do” inheritance?
Keywords: virtual, override A base class declares a method as
virtual A derived class declares a method as
override public/private =>
public/private/protected/internal Reference base class using “base.”
Inherited Classesclass First{ public virtual void methodA() { }}
class Second : First{ public override void methodA() { base.methodA(); }}
Considerations for Inheritance
Confirm “is-a” versus “has-a” relationship
Does adding one or more properties make sense?
Would an interface be more beneficial? Implicit and explicit casting between
inherited types Using the “as” operator instead of
casting to avoid exceptions
Abstract Classes
Abstract classes cannot be instantiated, and can only serve as a base class
Abstract methods and properties must be overridden in a derived classYou know the method or property exists for
every object of this type, but there is no implementation at this level of abstraction.
Sealed Classes
Sealed classes cannot be inherited Sealed methods and properties cannot
be overridden
Start thinking about how objects you need to model may inherit from one another.
Are there any obvious heirarchies, common attributes, or shared behavior?
Suggestions
Try to work through Exercises 14-1 and 14-2 in the book (p. 457)