Introduction to oop
- 2. What is OOP? • OOP is a design philosophy. It stands for Object Oriented Programming. Object-Oriented Programming (OOP) uses a different set of programming languages than old procedural programming languages (C, Pascal, etc.). Everything in OOP is grouped as self sustainable "objects". Hence, you gain reusability by means of four main object-oriented programming concepts. • In order to clearly understand the object orientation model, let’s take your “hand” as an example. The “hand” is a class. Your body has two objects of the type "hand", named "left hand" and "right hand". Their main functions are controlled or managed by a set of electrical signals sent through your shoulders (through an interface). So the shoulder is an interface that your body uses to interact with your hands. The hand is a well-architected class. The hand is being reused to create the left hand and the right hand by slightly changing the properties of it.
- 3. What is an Object? • An object can be considered a "thing" that can perform a set of related activities. The set of activities that the object performs defines the object's behavior. For example, the Hand (object) can grip something, or a Student(object) can give their name or address. • In pure OOP terms an object is an instance of a class.
- 4. What is a Class? • A class is simply a representation of a type of object. It is the blueprint, or plan, or template, that describes the details of an object. A class is the blueprint from which the individual objects are created. Class is composed of three things: a name, attributes, and operations. • public class Student { } • According to the sample given below we can say that the Student object, named objectStudent, has been created out of the Student class. • Student objectStudent = new Student();
- 6. classes • In order to manage the classes of a software system, and to reduce the complexity, system designers use several techniques, which can be grouped under four main concepts named • 1. Encapsulation • 2. Abstraction • 3. Inheritance • 4. Polymorphism.
- 7. What is Encapsulation (or Information Hiding)? • The encapsulation is the inclusion-within a program object-of all the resources needed for the object to function, basically, the methods and the data. • In OOP the encapsulation is mainly achieved by creating classes, the classes expose public methods and properties. • A class is kind of a container or capsule or a cell, which encapsulate a set of methods, attribute and properties to provide its indented functionalities to other classes. In that sense, encapsulation also allows a class to change its internal implementation without hurting the overall functioning of the system. • That idea of encapsulation is to hide how a class does its business, while allowing other classes to make requests of it.
- 8. What is Abstraction • Abstraction is an emphasis on the idea, qualities and properties rather than the particulars (a suppression of detail). The importance of abstraction is derived from its ability to hide irrelevant details and from the use of names to reference objects. • Abstraction is essential in the construction of programs. It places the emphasis on what an object is or does rather than how it is represented or how it works. Thus, it is the primary means of managing complexity in large programs. • While abstraction reduces complexity by hiding irrelevant detail
- 9. What is an Abstract class? • Abstract classes, which declared with the abstract keyword, cannot be instantiated. It can only be used as a super-class for other classes that extend the abstract class. • Abstract class is the concept and implementation gets completed when it is being realized by a subclass. In addition to this a class can inherit only from one abstract class (but a class may implement many interfaces) and and must override all its methods/properties that are declared to be abstract and may override virtual methods/ properties. • Abstract classes are ideal when implementing frameworks.
- 10. What is an Interface? • Interface can be used to define a generic template and then one or more abstract classes to define partial implementations of the interface. Interfaces just specify the method declaration (implicitly public and abstract) and can contain properties (which are also implicitly public and abstract). • Interface definition begins with the keyword interface. An interface like that of an abstract class cannot be instantiated. • If a class that implements an interface does not define all the methods of the interface, then it must be declared abstract and the method definitions must be provided by the subclass that extends the abstract class. In addition to this an interfaces can inherit other interfaces. • public interface ILogger { • bool IsThisLogError { get; } }
- 11. What is Polymorphism? • Polymorphisms is a generic term that means 'many shapes'. More precisely Polymorphisms means the ability to request that the same operations be performed by a wide range of different types of things. • In OOP the polymorphisms is achieved by using many different techniques named method overloading, operator overloading, and method overriding,
- 12. What is Method Overloading? • Method overloading is the ability to define several methods all with the same name. • public class MyLogger { public void LogError(Exception e) { // Implementation goes here } public bool LogError(Exception e, string message) { // Implementation goes here } }
- 13. What is Method Overriding? • Method overriding is a language feature that allows a subclass to override a specific implementation of a method that is already provided by one of its super-classes. • A subclass can give its own definition of methods but need to have the same signature and same name as the method in its super-class. This means that when overriding a method the subclass's method has to have the same name and parameter list as the super-class' overridden method.
- 14. example • using System; public class Complex { private int real; public int Real { get { return real; } } private int imaginary; public int Imaginary { get { return imaginary; } } public Complex(int real, int imaginary) { this.real = real; this.imaginary = imaginary; } public static Complex operator +(Complex c1, Complex c2) { return new Complex(c1.Real + c2.Real, c1.Imaginary + c2.Imaginary); } public override string ToString() { return (String.Format("{0} + {1}i", real, imaginary)); }}
- 15. Access modifiers • public • The type or member can be accessed by any other code in the same class or another class that references it. • private • The type or member can only be accessed by code in the same class or struct. • protected • The type or member can only be accessed by code in the same class or struct, or in a derived class.
- 16. Access modifier • Static • The static modifier on a class means that the class cannot be instantiated, and that all of its members are static. A static member has one version regardless of how many instances of its enclosing type are created. • A static class is basically the same as a non-static class, but there is one difference: a static class cannot be externally instantiated. In other words, you cannot use the new keyword to create a variable of the class type. Because there is no instance variable, you access the members of a static class by using the class name itself.