Virtual function is a function or method used to override the behavior of the function in an inherited class with the same signature to achieve the polymorphism. Virtual function defined in the base class and overridden in the inherited class. The Virtual function cannot be private, as the private functions cannot be overridden.
It is used to achieve runtime polymorphism. A pure virtual function is that function which have no definition. A pure virtual function have not definitions but we must override that function in the derived class, otherwise the derived class will also become abstract class. Constructor is a special type of member function which is used to initialize an object.
It is called when an object of the class is created. At the time of calling constructor, memory for the object is allocated in the memory. The constructor method having the argument list or parameter list is called as parameterized constructor as it initializes the fields with the values of the parameters. A copy constructor is that constructor which use existing object to create a new object. It copy variables from another object of the same class to create a new object. A static constructor is automatically called when the first instance is generated, or any static member is referenced.
The static constructor is explicitly declared by using a static keyword. However, the static constructor is not supported in Java.
Java enables us to declare a constructor as private. We can declare a constructor private by using the private access specifier. Note that if a constructor is declared private, we cannot create an object of the class. Instead, we can use this private constructor in Singleton Design Pattern. Destructor is a type of member function which is used to destroy an object. It is called automatically when the object goes out of scope or is explicitly destroyed by a call to delete.
It destroy the objects when they are no longer in use. The constructor method of the class may or may not have the argument list, and it has no return type specified and we also know that method overloading depends only on the argument list and not on the return type. Thus, we can say that the constructor method can be overloaded. I hope that after reading this article, your OOPs concept in Java has been quite clear.
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Save my name, email, and website in this browser for the next time I comment. You can download the PDF given at the end of the Article. What is OOPs? What are the basic features of OOPs? Why use OOPs? What is a class? What is an object? What is the difference between a class and an object?
What is the difference between a class and a structure? What is encapsulation? What are access specifiers? What is the difference between public, private and protected access modifiers? What is data abstraction? How to achieve data abstraction?
What is an abstract class? What is an interface? Differentiate between data abstraction and encapsulation. Can we create an instance of an abstract class? What is inheritance? Why we use inheritance? What is superclass? What is a subclass? What are the types of inheritance? What is single inheritance? What is multilevel inheritance? What is multiple inheritance? However, auto-implemented properties cannot be read-only or write-only. In Visual Basic, there are two ways to create a method: the Sub statement is used if the method does not return a value; the Function statement is used if a method returns a value.
A class can have several implementations, or overloads , of the same method that differ in the number of parameters or parameter types. In most cases you declare a method within a class definition. However, Visual Basic also supports extension methods that allow you to add methods to an existing class outside the actual definition of the class. Constructors are class methods that are executed automatically when an object of a given type is created.
Constructors usually initialize the data members of the new object. A constructor can run only once when a class is created. Furthermore, the code in the constructor always runs before any other code in a class. However, you can create multiple constructor overloads in the same way as for any other method.
Destructors are used to destruct instances of classes. In the. NET Framework, the garbage collector automatically manages the allocation and release of memory for the managed objects in your application. However, you may still need destructors to clean up any unmanaged resources that your application creates.
There can be only one destructor for a class. For more information about destructors and garbage collection in the. Events enable a class or object to notify other classes or objects when something of interest occurs. The class that sends or raises the event is called the publisher and the classes that receive or handle the event are called subscribers. For more information about events, how they are raised and handled, see Events. To declare events, use the Event Statement. To raise events, use the RaiseEvent Statement.
To specify event handlers using a declarative way, use the WithEvents statement and the Handles clause. To be able to dynamically add, remove, and change the event handler associated with an event, use the AddHandler Statement and RemoveHandler Statement together with the AddressOf Operator.
A class defined within another class is called nested. By default, the nested class is private. To create an instance of the nested class, use the name of the container class followed by the dot and then followed by the name of the nested class:. All classes and class members can specify what access level they provide to other classes by using access modifiers. For more information, see Access levels in Visual Basic. After instantiating a class, you can assign values to the instance's properties and fields and invoke class methods.
A shared member of the class is a property, procedure, or field that is shared by all instances of a class. Shared modules in Visual Basic have shared members only and cannot be instantiated. Objects can contain related data and code, which represent information about the thing you are trying to model, and functionality or behavior that you want it to have. Object data and often, functions too can be stored neatly the official word is encapsulated inside an object package which can be given a specific name to refer to, which is sometimes called a namespace , making it easy to structure and access; objects are also commonly used as data stores that can be easily sent across the network.
Let's consider a simple program that displays information about the students and teachers at a school. Here we'll look at OOP theory in general, not in the context of any specific programming language.
To start this off, we could return to our Person object type from our first objects article , which defines the generic data and functionality of a person. There are lots of things you could know about a person their address, height, shoe size, DNA profile, passport number, significant personality traits This is known as abstraction — creating a simple model of a more complex thing, which represents its most important aspects in a way that is easy to work with for our program's purposes.
From our class, we can create object instances — objects that contain the data and functionality defined in the class. From our Person class, we can now create some actual people:. When an object instance is created from a class, the class's constructor function is run to create it. This process of creating an object instance from a class is called instantiation — the object instance is instantiated from the class.
In this case we don't want generic people — we want teachers and students, which are both more specific types of people. In OOP, we can create new classes based on other classes — these new child classes also known as subclasses can be made to inherit the data and code features of their parent class , so you can reuse functionality common to all the object types rather than having to duplicate it.
Where functionality differs between classes, you can define specialized features directly on them as needed. This is really useful — teachers and students share many common features such as name, gender, and age, so it is convenient to only have to define those features once.
You can also define the same feature separately in different classes, as each definition of that feature will be in a different namespace. For example, a student's greeting might be of the form "Yo, I'm [firstName]" e. Note: The fancy word for the ability of multiple object types to implement the same functionality is polymorphism.
Just in case you were wondering. In the rest of the article, we'll start to look at how OOP theory can be put into practice in JavaScript. JavaScript uses special functions called constructor functions to define and initialize objects and their features.
They are useful because you'll often come across situations in which you don't know how many objects you will be creating; constructors provide the means to create as many objects as you need in an effective way, attaching data and functions to them as required. Let's explore creating classes via constructors and creating object instances from them in JavaScript.
First of all, we'd like you to make a new local copy of the oojs. The constructor function is JavaScript's version of a class.
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