Outline

1
Outline

• Review - Properties
• Properties allow to read and write class fields
• Implement a Property.
• Read-Only Property
• Write-Only Property.
• Define and use overloading methods
• Use Class variables and class methods
• i.e. static variables and methods
• Define and use arrays (text chapter 7)

2
Properties

• class Point
• private double x
• private double y
• public Point(double x, double y)
• this.x x
• this.y y
• public double getY()
• return y
• public setY(double y)
• this.y y

class Point private double x private double
y public Point(double x, double y) this.x
x this.y y public double Y get return
y set y value
getter
property
setter
get accessor is used in read context
set accessor is used in write context
3
Properties

• Point p1 new Point(1.0, 2.0)
• Point p2 new Point(-1.0, -2.0)
• p1.Y p2.Y

Read context, so get accessor of property is used
Write context, so set accessor of property is
used
4
Exercise
The code below uses property Y of class Point.
Where is get accessor of the property is used
and where is set accessor is used?

• Console.WriteLine(The Y coordinate is p1.Y)
• p1.Y double.Parse(Console.ReadLine())
• if ( p2.Y lt p1.Y)
• Console.WriteLine(point p2 is below p1)
• double v -p2.Y

5
Read-only and write-only properties

• Find out errors in the following code fragment

• class Student
• private int id
• private string passwd
• private bool registered
• public Student (int the_id)
• id the_id
• registered false
• passwd
• public string PassWord
• set passwd value
• public int ID

Student s1 new Student(000) Student s1 new
Student(111) s1.PassWord hello,world s2.Pas
sWord s1. Password s1.ID 222 int id
s2.ID Console.WriteLine(s1 state
s1.registered)
Write-only property
Read-only property
Read/write property
6
Define and use overloading methods

• We can use method overloading to define more than
  one method with the same name.
• Overloaded methods must have different parameter
  lists
• Example 5.1
• Overloaded constructors - BankAccount.cs
• Exercise write a method overload the Deposit
  method in BankAccount class.
• This method takes no parameter. And itll deposit
  100.
• Test it using example 5.2 TestBankAccount.cs

7
Class variables and class methods

• A class, we can define
• data fields
• constructor
• methods
• Non-static fields and methods must be used with
  the object prefix.
• Such fields or methods are called instance
  variables or instance methods
• Usage
• First declare and create an object of the class
• ObjectName.field_name
• ObjectName.method_name
• Static fields and methods must be used with the
  class prefix. Because they belong to the class,
  NOT objects.
• Such fields or methods are called class variables
  or class methods
• Usage
• ClassName.Static_field_name
• ClassName.Static_method_name

8
Class variables and class methods

• class Square
• private double length, width
• //Define a static variable recording the number
  of resizing operations
• private static int resize_times 0
• public Square (double l, double w)
• length l
• width w
• public Resize(double l1, double w1)
• length l
• width w1
• resize_times

class variable
Write a program which - creates two square
objects - resizes them several times - outputs
the total number of resizing operations.
class method
9
Difference of class variables(static) and
instance variables(non-static)

• class Square
• private double length, width
• private static int resize_times 0
• ..

Square s1 new Square(1.0,2.0) Square s1 new
Square(3.0,4.0)
resize_times
length width
length width
object referenced by s2
object referenced by s1
s1
s2
reference s1
reference s2
10
Arrays

• Define arrays
• int x 9,8,7 //initialize array elements in
  definition
• int y new int10 //define
• Array length
• int size1 x.Length
• int size2 y.Length
• Use array indices to access array elements
• index range from 0 to (array.Length-1)
• x0 x1 x2 0.0