Lecture 8

1. Get set property
class Thought
{
private int a;
public int xy {
get {
return a;
}
set {
a = value;
}
}
}
class Program
{
static void Main( string[] args ){
Thought t = new Thought();
t.xy = 23;
Console.WriteLine("value=“+t.xy);
Console.ReadLine();
}
}

2. Abstract Class
Motivation: if you think no object of a class should be
created, declare the class abstract
In general, an abstract class is a placeholder in a class
hierarchy that represents a generic concept
The use of abstract classes is a design decision; it helps us
establish common elements in a class that is too general to
instantiate
Vehicle
Car
Boat
Plane
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3. Abstract Classes: Syntax
Use the modifier abstract on a class header to declare an
abstract class, e.g.,
abstract class Vehicle
{
// …
public abstract void Move();
}
class Car : Vehicle
{ //…
public void Move()
{
Console.WriteLine( “Car is moving!” );
}
}
abstract class StaffMember
{
// …
public abstract double Pay();
}
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4. Abstract Class: Some Properties
An abstract class cannot be instantiated
but you can define a reference of an abstract class
Only abstract classes can contain abstract
methods
The child of an abstract class must override
the abstract methods of the parent, or it too
must be declared abstract
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5. C# Contains Many Other Features to
Further Refine the Definition of a Class
Sealed class or method
if you declare a class or method sealed, then the
class or method cannot be extended
Operator overloading
you can define operators for a class so that
operations look more like a normal arithmetic
operation
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6. Using Interface for Multiple Inheritance
Java/C# decision: single inheritance,
meaning that a derived class can have only
one parent class
To take the advantages of multiple
inheritance, Java/C# defines interfaces,
which give us the best aspects of multiple
inheritance without the complexity
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7. C# Interface
A C# interface is a collection of methods, and properties
it can actually include other types of definitions
These methods and properties have no implementation
An interface is used to formally define a set of methods that a
class will implement
An interface captures one aspect of a class
If class D is derived from class B, then you should feel comfortable in
saying an object of D is also a B
If class D implements interface I, then you should feel comfortable in
saying an object of D has I perspective
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8. Interfaces: Syntax
interface is a reserved word
public interface IComplexity
{
int
Level { get; set; }
}
public interface IDisplayAble
{
void Paint();
}
// inherits Question, implements two interfaces
class MultiChoice: Question, IComplexity, IDisplayAble
{
public void Paint() {...}
public int Level {...}
public string GetQuestionPart() {}
public string GetAnswerPart() {}
}
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9. Interfaces
Methods in an interface have public visibility by default
An interface cannot be instantiated
A class implements an interface by
stating so in the class header after :
A class can implement multiple interfaces: the interfaces
are separated by commas
If a class asserts that it implements an interface, it must
define all methods in the interface or the compiler will
produce errors
A class that implements an interface can implement
other methods as well
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10. Polymorphism via Interfaces
An interface name can be used as the type of
an object reference variable
IDoable obj;
The obj reference can be used to point to
any object of any class that implements the
IDoable interface
The version of doThis that the following line
invokes depends on the type of object that
obj is referring to:
obj.doThis();
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11. An Example
ISpeak guest;
guest = new Professor();
guest.Speak();
guest = Dog();
guest.Speak();
ISpeak special;
special = new Professor();
special.Pontificate(); // compiler error
ISpeak special;
special = new Professor();
((Professor)special).Pontificate();
public interface ISpeak
{
public void Speak();
}
class Faculty {…}
class Professor: Faculty, ISpeak
{
//
public void Speak()
{…}
public void Pontificate()
{…}
}
class Animal {}
class Dog: Animal, ISpeak
{
//
public void Speak()
{
…
}
}
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12. Exception Handing
Exception handling is an in built mechanism
in .NET framework to detect and handle run
time errors.
The .NET framework contains lots of standard
exceptions.
The exceptions are anomalies that occur
during the execution of a program.
They can be because of user, logic or system
errors.
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13. Exception Handing
If a user (programmer) do not provide a
mechanism to handle these anomalies, the
.NET run time environment provide a default
mechanism, which terminates the program
execution.
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14. Syntax
C# provides three keywords try, catch and
finally to do exception handling.
try
{
// Statement which can cause an exception.
}
catch(Type x)
{
// Statements for handling the exception
}
finally
{
//Any cleanup code
}
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15. Uncaught Exception
using System;
class MyClient
{
public static void Main()
{
int x = 0;
int div = 100/x;
Console.WriteLine(div);
}
}
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16. Exception handled
class MyClient
{
public static void Main()
{
int x = 0;
int div = 0;
try
{
div = 100/x;
Console.WriteLine("This line in not executed");
}
catch(DivideByZeroException de){
Console.WriteLine("Exception occured");
}
finally{
Console.WriteLine("Finally Block");
}
}}
Console.WriteLine("Result is {0}",div);
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17. Catching all Exception
using System;
class MyClient
{
public static void Main()
{
int x = 0;
int div = 0;
try
{
div = 100/x;
Console.WriteLine("Not executed line");
}
catch
{
Console.WriteLine("oException" );
}
Console.WriteLine("Result is {0}",div);
}
}
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18. Standard Exceptions
System.OutOfMemoryException
System.NullReferenceException
Syste.InvalidCastException
Syste.ArrayTypeMismatchException
System.IndexOutOfRangeException
System.ArithmeticException
System.DevideByZeroException
System.OverFlowException
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