C Sharp Programming/Encapsulation2

Properties

Properties encapsulate the control of an object's state.

For example, the following Customer class encapsulates a customer's name:

public class Customer
{ 
  // "private" prevents access of _name outside the Customer class:
  private string _name;   

  // The following property allows programmatic changes to _name:
  public string Name
  {
      set { this._name = value; }
      get { return this._name; }
  }
}

The above Name property has three important parts: the declaration, the set accessor, and the get accessor.

Property declaration

<access modifier> <type> <property name> 

public string Name

The access modifier determines who can manipulate this data. Properties can be scoped as public, private, protected, or internal.

The type determines what kind of type it can accept or return.

The property name declares the name used to access the property.

Accessors

Setting the Name property for the Customer class is done through the set accessor, defined using the set keyword.

Similarly, the get keyword creates a get accessor to encapsulate the logic to perform when clients retrieve the value of the property.

Above, the simple set accessor and get accessor make property behave very much like a simple field. That may not be the desired behavior. If not, we can add logic to check the value passed into the set accessor:

public string Name
       {
           set { 
                 if (value != null)
                    this._name = value;
               }
           get {                   
                 if (this._name != null)
                    return this._name;
                 else
                    return "John Doe";
               }
       }

Above, if the client requests to set the value to null, the set accessor does not change the field. Also, if the _name field hasn't yet been set, the get accessor returns a default value.

Using properties

Clients can use property much like they use simple class fields:

Customer customer = new Customer();

// this will not set the data.
customer.Name = "";

// since the field is not yet set, this will print out: "John Doe"
System.Console.WriteLine(customer.Name);

customer.Name = "Marissa";
System.Console.WriteLine(customer.Name);

The above code prints the following:

John Doe
Marissa

Accessibility levels

The various accessibility levels C# provides are, from most public to least:

Accessibility	Usage restriction
public	None.
internal	The containing assembly.
protected internal	The containing assembly or types derived from the containing class.
protected	The containing class or types derived from it.
private	The containing type.

If no accessibility level is specified, a default level is used. They are:

Type	Default accessibility
namespace	public (and the only allowed)
enum	public
class	private
interface	public
struct	private
(others)	internal

Note: namespace-level elements (e.g. a class declared directly under a namespace) cannot be declared as stricter than internal.