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In a variety of object-oriented programming languages, property is a member of the class that provides the procedures for operating on a data member of that class. Properties provide a higher level of encapsulation compared to public fields. Properties are intermediate between member code (methods) and member data (instance variables) of the class.
Support in languages
Programming languages that support properies include Delphi (programming language), Visual Basic and C#. Some object-oriented languages, such as C++ and Java, don't support properties, and require the programmer to define a pair of accessor and mutator methods instead.
In most languages, properties are implemented as a pair of accessor/mutator methods, but accessed using the same syntax as for public fields. Omitting a method from the pair yields a read-only or write-only property, the latter being rather uncommon.
In some languages with no built-in support for properties, a similar construct can be implemented as a single method that either returns or changes the underlying data, depending on the context of its invocation. Such techniques are used e.g. in Perl.
Example syntax
Delphi
type TPen = class private m_Color: Integer; function Get_Color: Integer; procedure Set_Color(RHS: Integer); public property Color: Integer read Get_Color write Set_Color; end; function TPen.Get_Color: Integer; begin Result := m_Color end; procedure TPen.Set_Color(RHS: Integer); begin m_Color := RHS end; // accessing: var pen: TPen; // ... pen.Color := not pen.ColorVisual Basic
' in a class named clsPen Private m_Color As Long Public Property Get Color() As Long Color = m_Color End Property Public Property Let Color(ByVal RHS As Long) m_Color = RHS End Property ' accessing: Dim pen As New clsPen ' ... pen.Color = Not pen.ColorC#
class CPen { private int m_Color; public int Color { get { return m_Color; } set { m_Color=value; } } } // accessing: CPen pen = new CPen(); // ... pen.Color = ~pen.Color;See also
"Property (programming)"