CLASS, STRUCT, INTERFACE - ThS. Nguyễn Hà Giang pdf

CLASS, STRUCT, INTERFACE
ThS. Nguyễn Hà Giang
1Nguyen Ha Giang -2009
Content
1.
Class definition
2. Constructor & destructor
3. Property
4. Indexer
5. Polymorphism
6. Downcast –Upcast
7. Abstract class –Sealed class
8. Struct
9. Interface
2Nguyen Ha Giang -2009
Class declaration
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[access modifier] class <class_name> [:base class, interfaces…]
{
// class body
}
Access modifier
public
protected
internal
protected internal
private (default)
Base class: only one class or not
Interface: implement some interfaces
Class declaration
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public class Student
{
// data member
…
// function member
…
}
Access modifier public
No base class
Default derive from
object (System.Object)
Class member
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Class
Constructor
Properties
Indexer
Delegate,
event
Method
Field,
const,
readonly
Nested
type
Constructor
•
Called when create object
• Same class name
• Class has default constructor which no

parameter
• Class has multiple constructor (overloading
constructor)
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Constructor
•
Default constructor
•No parameter
•Create object when has no any information
• Copy constructor
•Input parameter is another object
•Create new object like input object
• Other constructors
•One or more parameter
•Create new object with some information
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Constructor
•
Ex
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public class Student
{
// data member
string name;
int year;
float mark;
// function member
…
}
public Student()

{
name = “Ha Giang";
year = 1978;
mark = 5;
}
public Student(Student st)
{
name = st.name;
year = st.year;
mark = st.mark;
}
public Student(string sname)
{
name = sname;
}
Constructor
•
The private constructor prevents the class from
being created
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class Student
{
//
private Student()
{
}
}
class Program
{
static void Main(string[] args)

{
Student s = new Student();
}
}
Constructor
•
Constructor chaining
•Call one constructor from another constructor
•Usage
•base(parameter): call constructor of base class
•this(parameter): call a constructor in the current class
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<constructor of class A> : base(list of parameter)
<constructor of class A> : this(list of parameter)
Constructor
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class Person {
protected string name;
protected int year;
public Person(string name, intyear) {
this.name = name;
this.year= year;
}
}
class Student : Person {
float mark;
public Student(string name, intyear, float mark)
: base(name, year)
{
this.mark= mark;

}
}
Call base constructor
Constructor
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class Student
{
string name;
int year;
float mark;
public Student(string name, intyear)
{
this.name = name;
this.year= year;
}
public Student(string name, intyear, float mark)
: this(name, year)
{
this.mark= mark;
}
}
Call constructor
Destructor
•
Features of destructor
•A class can have one destructor only
•Destructor cannot be inherited or overloaded
•Destructor are invoked automatically
•Destructor can not have modifiers or parameters
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class Student
{
//…
~ Student()// destructor
{
//Code for cleanup resources
}
}
Instantiating an object
•
Declare
•Data member of class
•Variable of method
• Using “new” keyword
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Student st;
st
st= new Student(“Ha Giang”, 1978);
<Student>
st
Method
•
Methods are declared within a class by
•Access modifier
•Return value
•Name of method
•List of parameter
• Including
•Static method
•Non static method

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Method
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class Student {
static intnumber; // save number of objects
string name;
//constructor
public Student(string n) {
name = n;
number++; //increment 1
}
public void Show() {
Console.WriteLine("{0} ",name);
}
public static intNumberOfInstance() {
return number; // return number of objects
}
}
Method
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class Program
{
static void Main(string[] args)
{
Student s1 = new Student("Ha Giang");
Student s2 = new Student("Ngoc Thao");
Student s3 = new Student("Ha Nam");
s1.Show();
intnum = Student.NumberOfInstance();
Console.WriteLine("Number of objects: {0}", num);

Console.ReadLine();
}
}
Invoked by instance of class
Called directly from the class
Overload
•
Methods
•same name
• Different sets of parameters determined by
•The number
•Types
•Order of the parameter
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Overload
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class HagLib{
public void Swap(ref inta, ref intb) {
inttemp = a;
a = b;
b = temp;
}
public void Swap(ref long a, ref long b) {
long temp = a;
a = b;
b = temp;
}
public void Swap(ref float a, ref float b) {
float temp = a;
a = b;

b = temp;
}
}// end class
Different by type
of parameters
Virtual Method
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Employee
SaleEmployee
Virtual Method
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class Employee {
public void CalculatePay()
{
Console.WriteLine("Employee.CalculatePay");
}
}
class SaleEmployee: Employee {
public void CalculatePay()
{
Console.WriteLine("SaleEmployee.CalculatePay");
}
}
Employee e = new Employee();
SaleEmployee s = new SaleEmployee();
e.CalculatePay();
s.CalculatePay();
e = new SaleEmployee();
e.CalculatePay();
Why not polymorphism?

Virtual Method
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class Employee {
public virtual void CalculatePay()
{
Console.WriteLine("Employee.CalculatePay");
}
}
class SaleEmployee: Employee {
public override void CalculatePay()
{
Console.WriteLine("SaleEmployee.CalculatePay");
}
}
Employee e = new Employee();
SaleEmployee s = new SaleEmployee();
e.CalculatePay();
s.CalculatePay();
e = new SaleEmployee();
e.CalculatePay();
Polymorphism!
Property
•
Provide a flexible mechanism to read, write or
compute the values of private fields
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Private member
private string name
-GetName()
-SetName(…)

Private member
private string name
Property: NAME
Getter/Setter method Property
Property
•
Properties as “smart” fields
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[modifers]<type><property-name>
{
[set{<accessor-body>}]
[get{<accessor-body>}]
}
[modifers]<type><property-name>
{
set {<accessor-body>}
}
[modifers]<type><property-name>
{
get {<accessor-body>}
}
Write-only property Read-only property
Property
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class Employee {
// fields
private string name;
private float salary;
// properties
public string NAME {

get {
return name;
}
set {
name = value;
}
}
public float SALARY {
get {
return salary;
}
}
}
Read write property
Read only property