Classic Design Patterns Book By Gof Pdf
Introduction to Programming with C# / Java Books » Chapter 2. Object- Oriented Programming Principles (OOP)In this chapter we will familiarize ourselves with the principles of object- oriented programming: class inheritance, interface implementation, abstraction of data and behavior, encapsulation of data and class implementation, polymorphism and virtual methods. We will explain in details the principles of cohesion and coupling.
We will briefly outline object- oriented modeling and how to create an object model based on a specific business problem. We will familiarize ourselves with UML and its role in object- oriented modeling. Finally, we will briefly discuss design patterns and illustrate some of those that are widely used in practice. Content. Video. Presentation. Mind Maps. We introduced classes and objects in the chapter . Let’s shortly review them again.
Classes are a description (model) of real objects and events referred to as entities. An example would be a class called . An example would be a set of grades. Classes also expose behavior known in programming as methods.
An example would be sitting an exam. Methods and properties can be visible only within the scope of the class, which declared them and their descendants (private / protected), or visible to all other classes (public).
Objects are instances of classes. For example, John is a Student and Peter is also a Student. Object- oriented programming is the successor of procedural (structural) programming. Procedural programming describes programs as groups of reusable code units (procedures) which define input and output parameters. Procedural programs consist of procedures, which invoke each other. The problem with procedural programming is that code reusability is hard and limited – only procedures can be reused and it is hard to make them generic and flexible. There is no easy way to work with abstract data structures with different implementations.
The object- oriented approach relies on the paradigm that each and every program works with data that describes entities (objects or events) from real life. For example: accounting software systems work with invoices, items, warehouses, availabilities, sale orders, etc. This is how objects came to be. They describe characteristics (properties) and behavior (methods) of such real life entities. The main advantages and goals of OOP are to make complex software faster to develop and easier to maintain. OOP enables the easy reuse of code by applying simple and widely accepted rules (principles).
An agency of the U.S. Department of Commerce. Conducts environmental research. Modern C++ Design (Andrei Alexandrescu) A groundbreaking book on advanced generic programming techniques. Introduces policy-based design, type lists, and.
The builder pattern is an object creation software design pattern. Unlike the abstract factory pattern and the factory method pattern whose intention is to enable. There have been several questions already posted with specific questions about dependency injection, such as when to use it and what frameworks are there for it.
Let’s check them out. In order for a programming language to be object- oriented, it has to enable working with classes and objects as well as the implementation and use of the fundamental object- oriented principles and concepts: inheritance, abstraction, encapsulation and polymorphism. Let’s summarize each of these fundamental principles of OOP: - Encapsulation. We will learn to hide unnecessary details in our classes and provide a clear and simple interface for working with them.- Inheritance.
We will explain how class hierarchies improve code readability and enable the reuse of functionality.- Abstraction. Windows Media Player 11 Wine Install Mono. We will learn how to work through abstractions: to deal with objects considering their important characteristics and ignore all other details.- Polymorphism. We will explain how to work in the same manner with different objects, which define a specific implementation of some abstract behavior. Some OOP theorists also put the concept of exception handling as additional fifth fundamental principle of OOP. We shall not get into a detailed dispute about whether or not exceptions are part of OOP and rather will note that exceptions are supported in all modern object- oriented languages and are the primary mechanism of handling errors and unusual situations in object- oriented programming. Exceptions always come together with OOP and their importance is explained in details in the chapter .
It allows a class to . For example, a lion belongs to the biological family of cats (Felidae). All cats that have four paws, are predators and hunt their prey. This functionality can be coded once in the Felidae class and all its predators can reuse it – Tiger, Puma, Bobcat, etc. Inheritance is described as is- kind- of relationship, e. Tiger is kind of Animal.
How Does Inheritance Work in . NET? Inheritance in . NET is defined with a special construct in the class declaration. In . NET and other modern programming languages, a class can inherit from a single class only (single inheritance), unlike C++ which supports inheriting from multiple classes (multiple inheritance). This limitation is necessitated by the difficulty in deciding which method to use when there are duplicate methods across classes (in C++, this problem is solved in a very complicated manner). Driver Hp Laserjet 1200 Vista. In . NET, classes can inherit multiple interfaces, which we will discuss later. The class from which we inherit is referred to as parent class or base class / super class.
Inheritance of Classes – Example. Let’s take a look at an example of class inheritance in . NET. This is how a base class looks like: Felidae. Felidae is latin for . The keyword indicates that the base class must be used and allows access to its methods, constructors and member variables. Using base(), we can call the constructor of the base class.
Using base. Method(. Using base. field we can get the value of a member variable from the base class or assign a different one to it. In . NET, methods inherited from the base class and declared as virtual can be overridden. This means changing their implementation; the original source code from the base class is ignored and new code takes its place. More on overriding methods we will discuss in . Using the keyword is required only if we have an overridden method or variable with the same name in the inheriting class.
The keyword base can be used explicitly for clarity. Such source code is easier to read, because we know where to look for the method in question.
Bear in mind that using the keyword this is not the same. It can mean accessing a method from the current, as well as the base class. You can take a look at the example in the section about access modifiers and inheritance. There it is clearly explained which members of the base class (methods, constructors and member variables) are accessible. Constructors with Inheritance.
When inheriting a class, our constructors must call the base class constructor, so that it can initialize its member variables. If we do not do this explicitly, the compiler will place a call to the parameterless base class constructor, . Here is an example: publicclass.
Extending. Class : Base. Class. The omission of such a call will result in a compile- time error. If a class has private constructors only, then it cannot be inherited. If a class has private constructors only, then this could indicate many other things. For example, no- one (other than that class itself) can create instances of such a class. Actually, that’s how one of the most popular design patterns (Singleton) is implemented. The Singleton design pattern is described in details at the end of this chapter.
Constructors and the Keyword . It does not have a default constructor.
Let’s examine a class inheriting from Lion: African. Lion. cspublicclass. African. Lion : Lion. Try it. Calling the constructor of a base class happens outside the body of the constructor. The idea is that the fields of the base class should be initialized before we start initializing fields of the inheriting class, because they might depend on a base class field.
Access Modifiers of Class Members and Inheritance. Let’s review: in the . Regarding members of a class (methods, properties and member variables) we examined the modifiers public, private and internal. Actually, there are two other modifiers: protected and protectedinternal.
This is what they mean: - protected defines class members which are not visible to users of the class (those who initialize and use it), but are visible to all inheriting classes (descendants).- protected internal defines class members which are both internal, i. In this language, it often becomes necessary to code classes, which must work with objects of any type. C++ solves this problem in a way that is not considered strictly object- oriented (by using void pointers).
The architects of . NET take a different approach. They create a class, which all other classes inherit (directly or indirectly).
All objects can be perceived as instances of this class. It is convenient that this class contains important methods and their default implementation. This class is called Object (which is the same as object and System.
Object). In . NET every class, which does not inherit a class explicitly, inherits the system class System. Object by default. The compiler takes care of that. Every class, which inherits from another class indirectly, inherits Object from it.
This way every class inherits explicitly or implicitly from Object and contains all of its fields and methods. Because of this property, every class instance can be cast to.
Object. A typical example of the advantages of implicit inheritance is its use with data structures, which we saw in the chapters on data structures. Untyped list structures (like System. Collections. Array. List) can hold all kinds of objects, because they treat them as instances of the class Object. The generic types (generics) have been provided specifically for working with collections and objects of different types (generics are further discussed in the chapter .
They allow creating typified classes, e. These classes are part of the . NET framework; they are available wherever .
NET is supported. These classes are referred to as Common Type System (CTS). NET is one of the first frameworks, which provide such an extensive set of predefined classes. A lot of them work with Object so that they can be used in as many situations as possible.