Virtual, sealed, override, and abstract keywords

Question

Hi Friends, In what situations we use virtual, sealed, override, and abstract keywords?

Senthilkumar · Answer

Hi akshay, Abstract method: When a class contains an abstract method, that class must be declared as abstract. The abstract method has no implementation and thus, classes that derive from that abstract class, must provide an implementation for this abstract method. Virtual method: A class can have a virtual method. The virtual method has an implementation. When you inherit from a class that has a virtual method, you can override the virtual method and provide additional logic, or replace the logic with your own implementation. When to use what: In some cases, you know that certain types should have a specific method, but, you don't know what implementation this method should have. In such cases, you can create an interface which contains a method with this signature. However, if you have such a case, but you know that implementors of that interface will also have another common method (for which you can already provide the implementation), you can create an abstract class. This abstract class then contains the abstract method (which must be overriden), and another method which contains the 'common' logic. A virtual method should be used if you have a class which can be used directly, but for which you want inheritors to be able to change certain behaviour, although it is not mandatory. Only abstract classes can have abstract members. A non-abstract class that inherits from an abstract class must override its abstract members. An abstract member is implicitly virtual. An abstract member cannot provide any implementation (abstract is called pure virtual in some languages). Sealed classes cannot be derived from. Does the sealed keyword improve the performance of method calls? This C# keyword prevents derivation. And it has an impact on performance in some contexts.

MuthuMari M · Answer

Hi, The virtual keyword enables a class to be overridden. If it has to be prevented from being overridden, then the sealed keyword needs to be used. If the keyword virtual is not used, members of the class can even then be overridden. However, its usage is advised for making the code meaningful. The override keyword is used to override the virtual method in the base class. Abstract keyword is used to modify a class, method or property declaration. You cannot instantiate an abstract class or make calls to an abstract method directly. An abstract virtual method means that the definition of the method needs to be given in the derived class. thanks. If this post is useful then mark it as " Accepted Answer "

Kunal Vaishya · Answer

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable{mso-style-name:"Table Normal";mso-tstyle-rowband-size:0;mso-tstyle-colband-size:0;mso-style-noshow:yes;mso-style-priority:99;mso-style-qformat:yes;mso-style-parent:"";mso-padding-alt:0in 5.4pt 0in 5.4pt;mso-para-margin:0in;mso-para-margin-bottom:.0001pt;mso-pagination:widow-orphan;font-size:11.0pt;font-family:"Calibri","sans-serif";mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:"Times New Roman";mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;} Abstract Class An abstract class is a class with at least one method defined as abstract. This type of class cannot be instantiated. An abstract class can have one or more abstract methods and properties and other methods and properties like normal classes. Partial Class A class defined in two or more files is called a partial class. The keyword partial is used to define the class. When working on large projects, spreading a class over separate files allows multiple programmers to work on it simultaneously. During compile time all the partial class are compiled into one type only. Sealed Class A sealed class is a class that cannot be inherited. Sealed classes are used to restrict the inheritance feature of object oriented programming.

Virtual, sealed, override, and abstract keywords

Answers (3)