Getter and Setter Methods

Transcription

1 Example 1 namespace ConsoleApplication14 public class Student public int ID; public string Name; public int Passmark = 50; class Program static void Main(string[] args) Student c1 = new Student(); Console.WriteLine("please..enter the student's ID: "); c1.id=int.parse(console.readline()); Console.WriteLine("please..enter the student's name: "); c1.name = Console.ReadLine(); Console.WriteLine(c1.ID +" "+c1.name); The problems with this example are: 1- ID should always be non-negative number. 2- Name cannot be set to NULL 3- If student name is missing No name should be returned 4- Passmark should be read only. 5-The main problem is (public fields)

2 To solve the problems like these we can use the encapsulation concept What does Encapsulation mean? Encapsulation is an Object Oriented Programming concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse. Data encapsulation led to the important OOP concept of data hiding. Getter and Setter Methods Programming languages that do not have properties use getter and setter methods to encapsulate and protect fields.

3 Example 2 (Encapsulation using Getter and Setter Methods) namespace ConsoleApplication14 public class Student private int ID; private string Name; private int Passmark = 50; public void setid (int id) if (id<0) Console.WriteLine("please enter greater than or equal 0"); else this.id = id; public int getid() if (ID<0) Console.WriteLine("the Id is less than 0"); return this.id;

4 public void setname(string x) if (string.isnullorempty(x)) Console.WriteLine("you did not enter the name"); else this.name = x; public string getname() if (string.isnullorempty(name)) return "No Name"; else return this.name; public int getpassmark() return this.passmark;

5 class Program static void Main(string[] args) Student c1 = new Student(); Console.WriteLine("please..enter the student's ID: "); int x = int.parse(console.readline()); c1.setid(x); Console.WriteLine("please..enter the student's Name: "); string y = Console.ReadLine(); c1.setname(y); Console.WriteLine("the student id is : " + c1.getid()); Console.WriteLine("the student name is : " + c1.getname()); Console.WriteLine("the passmark is : " + c1.getpassmark()); In this example we use the (setid), (getid), (setname), (getname) and (getpassmark) methods to encapsulate (ID), (Name) and (Passmark) class fields As a result, we have better control on what gets assigned and returned from the (ID), (Name) and (Passmark) fields. Encapsulation is one of the primary concepts of object oriented programming.

6 Properties In C# to encapsulate and protect fields we use properties. We use get and set accessor to implement properties A property with both get and set accessor is a READ/WRITE property. A property with only get accessor is a READ only property. A property with only set accessor is a WRITE only property. The advantages of properties over traditional get() and set() methods is that, you can access them as if they were public fields Class Object Object Attributes Methods Constructors Properties Procedure Function

7 Example 3 (encapsulation using properties) namespace ConsoleApplication13 class Program static void Main(string[] args) Car ca1 = new Car(); ca1.color_property = "red"; Console.WriteLine(ca1.Color_property); ca1.typing(); Console.ReadKey(); public class Car //Fields int Id; string Color; string Model; //Properties public int Id_property get return Id; set Id = value; public string Color_property get return Color; set Color = value;

8 public string Model_property get return Model; set Model = value; //Constructors public Car(int id, string color, string model) Id = id; Color = color; Model = model; public Car( ) Id = 55; Color = "Black"; Model = "Kia"; //Methods public void typing () Console.WriteLine(Id); Console.WriteLine(Color); Console.WriteLine(Model);

9 Example 4 (encapsulation using properties) namespace ConsoleApplication16 class Program static void Main(string[] args) Student c1 = new Student(); Console.WriteLine("please..enter the student's ID: "); int x = int.parse(console.readline()); c1.id_property=x; Console.WriteLine("please..enter the student's Name: "); string y = Console.ReadLine(); c1.name_property=y; Console.WriteLine("the student id is : " + c1.id_property); Console.WriteLine("the student name is : " + c1.name_property); Console.WriteLine("the passmark is : " + c1.passmark_property);

10 public class Student private int ID; private string Name; private int Passmark = 50; public int ID_Property set if (value < 0) Console.WriteLine("please enter greater than or equal 0"); else this.id = value; get if (ID < 0) Console.WriteLine("the Id is less than 0"); return this.id;

11 public string Name_Property set if (string.isnullorempty(value)) Console.WriteLine("you did not enter the name"); else this.name = value; get if (string.isnullorempty(name)) return "No Name"; else return this.name; public int Passmark_Property get return this.passmark;

12 Auto-Implemented Properties If there is no additional logic in the property accessors, then we can use auto-implemented properties Auto-implemented properties reduce the amount of code that we have to write. When we use auto-implemented properties, the compiler creates a private field that we can use only be accessed through the property s get and set accessors.

13 Example 4 (encapsulation using auto-implemented properties) namespace ConsoleApplication17 class Program static void Main(string[] args) Employee emp = new Employee(); emp.name_property = "Mark"; emp.address_property = "London"; emp. _property = "mark@gmail.com"; Console.WriteLine(emp.Name_property); Console.WriteLine(emp.Address_property); Console.WriteLine(emp. _property); public class Employee public string Name_property get; set; public string Address_property get; set; public string _property get; set;