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Abstraction◄╣

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► KB ► To/From Guides ► C# ► Statements

Abstraction (Cross Ref > Statements)

By Mike Prestwood

C# versus Delphi Prism: A side by side comparison between C# and Delphi Prism.

OOP Details

More object oriented (OO) stuff.

Abstraction

[Other Languages]

General Info: Abstract Class / Abstract Member

An abstract class member is a member that is specified in a class but not implemented. Classes that inherit from the class will have to implement the abstract member. Abstract members are a technique for ensuring a common interface with descendant classes. An abstract class is a class you cannot instantiate. A pure abstract class is a class with only abstract members.

Languages Focus

Abstraction is supported at various levels with each language. A language could enforce abstraction at the class level (either enforcing a no-instantiation rule or a only abstract members rule), and with class members (member methods and/or properties).

C#: abstract, override

C# supports abstract class members and abstract classes using the abstract modifier.

An abstract class is a class with one or more abstract members and you cannot instantiate an abstract class. However, you can have additional implemented methods and properties.

An abstract member is either a method (implicitly virtual), property, indexer, or event in an abstract class. You can add abstract members ONLY to abstract classes using the abstract keyword. Then you override it in a descendant class with Override.

Syntax Example:

abstract public class Cyborg : System.Object

  abstract public void Speak(string pMessage);

public class Series600 : Cyborg

  public override void Speak(string pMessage)

    MessageBox.Show(pMessage);

C# Abstraction (abstract, override) 1 certification question.

Delphi Prism: abstract, override

Prism supports abstract class members and abstract classes using the abstract keyword.

An abstract class is a class with one or more abstract members and you cannot instantiate an abstract class. However, you can have additional implemented methods and properties.

An abstract member is either a method (method, procedure, or function), a property, or an event in an abstract class. You can add abstract members ONLY to abstract classes using the abstract keyword.

Alternatively, you can use the empty keyword in place of abstract if you wish to instantiate the abstract class. Then you override it in a descendant class with Override.

Syntax Example:

Cyborg = public abstract class(System.Object)
public
  //You can put "virtual; abstract;"

  //but it's implied with just "abstract;"

  method Speak(pMessage: String); abstract; 
  method Walk; virtual; abstract;
end;

Series600 = public class(Cyborg)
public
  procedure Speak(pMessage: String); override;
  procedure Walk; override;
end;

Delphi Prism Abstraction (abstract, override)