1. Class & Object
蔡柏灃

2. Object Oriented Programming
Basic concepts
Everything is an object
Blueprint and its realization
Ex1: A building
Ex2: A dog
Encapsulation
Inheritance
Polymorphism

3. Encapsulation Information of objects should be encapsulated
Data and corresponding accessing methods
Check and constrain accessing (access-modifiers)
Safety and reusability

4. Class & Object Class Object 1 class  lots of objects !
An user-defined type
Data (Properties) & Behaviors (Methods)
The Main()
Object
An entity of specific characteristics/functions existing in the memory – Normally, you are using objects not classes !
The new keyword
The dot ( . ) operator
1 class  lots of objects !

5. Access modifiers
It is strongly recommended to put the modifiers EXPLICITLY !!

6. Examples Example 4_1 Example 4_1_modified (access modifiers)
We build a time class and provide a method to display the time message
Example 4_1_modified (access modifiers)
Not a good example (public on variables)
Getter and setter
Property (introduce later)

7. Property Property is used to access the private variables
Getter: only provide get
You have to return
Setter: only provide set
Keyword value
Example 4_1_modified_2

8. using System;
namespace example4_1 {
public class Time
// private variables
private int Year = 2008;
private int Month = 1;
private int Date = 12;
private int Hour = 8;
private int Minute = 0;
private int Second = 0;
// public methods
public void DisplayCurrentTime( )
Console.WriteLine("Time --> {0}/{1}/{2} AM {3}:{4}:{5}", Year, Month, Date, Hour, Minute, Second); }
// properties
public int YEAR
get { return Year; }
set { Year = value; }
public int MONTH
get { return Month; }
set { Month = value; }
public class Tester
static void Main( )
Time t = new Time( );
t.YEAR = 2007;
t.MONTH = 11;
t.DisplayCurrentTime( );

9. Exercise 10 A simple personal telephone book
Please build a class that records your friends’ names and mobile phone numbers
Provide a display function that displays these messages

10. Constructors
It is used to initialize an object when it is firstly constructed by CLR
Every class has at least a constructor
If you don’t provide one, an empty constructor is provided automatically and implicitly
If you provide one, this default one will no longer exist
Should always has the same name as the class
Public
No return (not even void)
Example 10_modified
Keyword this

11. Exercise 11 A simple calculator
Please try to write a simple calculator that provides some basic arithmetic operations for two integer inputs
Max
Min
Mean
Static methods

12. A system time displayer (example 4_3)
System.DatTime class
Provided by C#
Used to store time
System.DateTime.Now is a property to get the current time
Don’t you don’t have to new anything?
Keyword static
You can access the methods or properties by ClassName.xxx
static to static

13. static members
Once you put the static keyword on you class member, it will be kept in the memory
You don’t have to new any object in order to use it
There is only one static member for all of you objects
No copies

14. Telephone book counter
How do you keep a counter that records the number of your friends recorded in the phone book ?
Example 10_modified_2

15. Exercise 12 Cats and dogs adoption system
Please write a system that keeps the numbers of cats and dogs and provides functions that modifies these numbers when any cat or dog is adopted or newly coming
catAdopted(int number)
catNew(int number)
Property CatNumber …