| 1 |
Although an abstract class is similar to a non-abstract class, some important differences exist. For one thing, you cannot create an instance of an abstract class with the new keyword. For example, the following statement will raise a compiler error. |
| 2 |
Interfaces are the constructs that were created to get away with the multiple inheritance problem and can have abstract methods, default definitions and static final variables. |
| 3 |
An abstract class allows you to do both declare (using abstract methods) as well as define (using full method implementations) the behavior you want the class to have. And a regular class only allows you to define, not declare, the behavior or actions you want the class to have. |
| 4 |
The main difference then is an interface has no implementation at all (only methods without a body) while abstract classes can have members and methods with a body as well, i.e. can be partially implemented. |
| 5 |
If you have some common methods that can be used by multiple classes go for abstract classes. Else if you want the classes to follow some definite blueprint go for interfaces. |
| 6 |
Interface: It is a keyword and it is used to define the template or blue print of an object and it forces all the sub classes would follow the same prototype,as for as implementation, all the sub classes are free to implement the functionality as per it's requirement. |
| 7 |
A child class can define abstract methods with the same or less restrictive visibility, whereas class implementing an interface must define all interface methods as public. Abstract Classes can have constructors but not interfaces. |
| 8 |
A concrete child class of an Abstract Class must define all the abstract methods. An Abstract child class can have abstract methods. An interface extending another interface need not provide default implementation for methods inherited from the parent interface. |
| 9 |
While abstract classes and interfaces are supposed to be different concepts, the implementations make that statement sometimes untrue. Sometimes, they are not even what you think they are. |
| 10 |
An interface is a contract: The guy writing the interface says, "hey, I accept things looking that way", and the guy using the interface says "OK, the class I write looks that way". |
| 11 |
Abstract classes look a lot like interfaces, but they have something more: You can define a behavior for them. It's more about a guy saying, "these classes should look like that, and they have that in common, so fill in the blanks!". |
| 12 |
An interface is an empty shell. There are only the signatures of the methods, which implies that the methods do not have a body. The interface can't do anything. It's just a pattern. |
| 13 |
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 behavior, although it is not mandatory. |
| 14 |
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. |
| 15 |
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. |
| 16 |
A virtual method is a method that can be overridden in a derived class using the override, replacing the behavior in the superclass. If you don't override, you get the original behavior. If you do, you always get the new behavior. |
| 17 |
Basically, you would use a virtual method if you have the 'default' implementation of it and want to allow descendants to change its behavior. With an abstract method, you force descendants to provide an implementation. |
| 18 |
An abstract method is a method that must be implemented to make a concrete class. The declaration is in the abstract class (and any class with an abstract method must be an abstract class) and it must be implemented in a concrete class. |
| 19 |
An abstract function has no implementation and it can only be declared on an abstract class. This forces the derived class to provide an implementation. A virtual function provides a default implementation and it can exist on either an abstract class or a non-abstract class. |
| 20 |
I would say if we are implementing an abstract class, you must have to override the abstract methods from the base abstract class. Because implementing the abstract method is with override key word. Similar to Virtual method. |
| 21 |
It is not necessary that an abstract method has to be implemented in a child class, if the child class is also abstract. An abstract method cant be a private method. An Abstract method cant be implemented in the same abstract class. |
| 22 |
Regarding virtual function: When you put a virtual method in the parent class you are saying to the derived classes : Hey there is a functionality here that do something for you. If this is useful for you just use it. If not, override this and implement your code, even you can use my implementation in your code! |
| 23 |
Regarding abstract method: When you put an abstract method in the parent class actually your are saying to the child classes: Hey note that you have a method signature like this. And if you wanna to use it you should implement your own! |
| 24 |
Abstract method: sub classes are forced to implement their own FireEscape method. With a virtual method, you have a basic plan waiting for you, but can choose to implement your own if it's not good enough. |
| 25 |
Late binding means that we use the name, but defer the mapping. In other words, we create or mention the name first, and let some subsequent process handle the mapping of code to that name. |
| 26 |
A virtual function, is basically saying look, here's the functionality that may or may not be good enough for the child class. So if it is good enough, use this method, if not, then override me, and provide your own functionality. |
| 27 |
An abstract function cannot have functionality. You're basically saying, any child class MUST give their own version of this method, however it's too general to even try to implement in the parent class. |
| 28 |
Before coding a project, design it by using post-it notes and a dry-erase board. This will make good practice until you get the hang of this. Think of your specific object, function, property. Each of those items will have its own post-it note. |
| 29 |
By practicing how to design a system, you'll start to get a natural feel for object relationships. Code is just a by-product of design. Draw diagrams and model your application in a purely non-code form. What are the relationships? How do your models interact? Don't even think about the code. |
| 30 |
Let's compare OOP with chocolate molds. The first thing you have to do to make some chocolates, you need to build its mold. The mold will have some characteristics for the future chocolates like shape, size, etc. depending on how you create the mold the future chocolates will be. |
| 31 |
Object Oriented Programming is the art of code to some, and a really hostile programming environment to others. OOP is basically when you use constructors or classes to define objects. OOP is beneficial in my profession, because of its developed design patterns such as inheritance and encapsulation. |
| 32 |
A class variable is any field declared with the static modifier; this tells the compiler that there is exactly one copy of this variable in existence, regardless of how many times the class has been instantiated. A field defining the number of gears for a particular kind of bicycle could be marked as static since conceptually the same number of gears will apply to all instances. |
| 33 |
It pays to remember: OO is not an end in itself. The point of OO is to make development and, especially, maintenance of code easier over the lifetime of the product. Beware of the "OO for OO's sake" mindset. |
| 34 |
When it comes down to it classes are a way to separate complex systems into simple parts that interact with each other. Try to create classes where otherwise you would be repeating yourself. |
| 35 |
An object is defined by a triple (OID, type constructor, state) where OID is the unique object identifier, type constructor is its type (such as atom, tuple, set, list, array, bag, etc.) and state is its actual value. |
| 36 |
Yes, the latest versions of PHP are object oriented. That is, you can write classes yourself, use inheritance, and where appropriate, the built in functionality is built in objects too (like MySQL features). |
| 37 |
The magic is that in JavaScript a function reference also has a secret reference to the closure it was created in — similar to how delegates are a method pointer plus a secret reference to an object. |
| 38 |
There is a critical difference between a C pointer to a function and a JavaScript reference to a function. In JavaScript, you can think of a function reference variable as having both a pointer to a function as well as a hidden pointer to a closure. |
| 39 |
A closure is one way of supporting first-class functions; it is an expression that can reference variables within its scope (when it was first declared), be assigned to a variable, be passed as an argument to a function, or be returned as a function result. |
| 40 |
JavaScript is a very good language to write object oriented web apps. It can support OOP because supports inheritance through prototyping also properties and methods. You can have polymorphism, encapsulation and many sub-classing paradigms. |
| 41 |
Unlike most object-oriented languages, JavaScript (before ECMA 262 Edition 4, anyway) has no concept of classes, but prototypes. As such, it is indeed somewhat subjective whether to call it object-oriented or not. |
| 42 |
Polymorphism is a non-issue in Javascript, as it doesn't much care about types at all. The only core OO feature not directly supported by the syntax is inheritance, but that can easily be implemented. |
| 43 |
Languages do not need to behave exactly like Java to be object-oriented. Everything in Javascript is an object; compare to C++ or earlier Java, which are widely considered object-oriented to some degree but still based on primitives. |
| 44 |
JavaScript is Object-Based, not Object-Oriented. The difference is that Object-Based languages don't support proper inheritance, whereas Object-Oriented ones do. There is a way to achieve 'normal' inheritance in JavaScript, but the basic model is based on prototyping. |
| 45 |
Everything in javascript is an object - classes are objects, functions are objects, numbers are objects, objects objects objects. It's not as strict about typing as other languages, but it's definitely possible to write OOP JS. |
| 46 |
While object-oriented programming languages encourages development focus on taxonomy and relationships, prototype-based programming languages encourages to focus on behavior first and then later classify. |
| 47 |
Implementing an interface allows a class to become more formal about the behavior it promises to provide. Interfaces form a contract between the class and the outside world, and this contract is enforced at build time by the compiler. |
| 48 |
JavaScript is a prototype-based programming language (probably prototype-based scripting language is more correct definition). It employs cloning and not inheritance. A prototype-based programming language is a style of object-oriented programming without classes. |
| 49 |
An OO programming language must have objects, method, property, classes, encapsulation, aggregation, inheritance and polymorphism. You could implement all this points, but JavaScript has not them. |
| 50 |
JavaScript has not changed for many years, but new programmers want to show JavaScript is an OO programming language. Why? JavaScript is a powerful language, but is not an OO programming language. |
| 51 |
What confuses me to no end in Javascript is that you can't even use function names, because you run the risk of having that same function name somewhere else in any of the external libraries that you're using. Some argue that JavaScript is not truly object oriented because it does not provide information hiding. That is, objects cannot have private variables and private methods: All members are public. |
| 52 |
For the record, JavaScript is not unique in this regard. Python also has no mechanism to enforce encapsulation. All members of a Python object are effectively public, and Python only uses naming conventions to indicate that a member should be treated as "private". But no one questions whether or not Python is an OO language. |
| 53 |
Encapusation requires storing private data on the execution context created when constructing the object. Members added to the prototype do not have access to this execution context and hence can not access the encapsulated data. |
| 54 |
Typeclasses are not a mechanism for implicit conversion to other types. They're a description of a set of functions defined for a type so as to provide a form of polymorphism. The closest thing from Java-style OOP would be interfaces, though Haskell typeclasses have some important differences. |
| 55 |
Functional Programming, in Haskell or even in Scala, can allow substitution through more general mechanism of type classes. Mutable internal state is either discouraged or forbidden. Encapsulation of internal representation can also be achieved. |
| 56 |
Take for example C#. You could say it's mostly OOP, but there are many FP concepts and constructs. If you consider Linq, the most important constructs that permit Linq to exist are functional in nature: lambda expressions. |
| 57 |
Even combining both Javascript and object oriented programming allows developers to write codes that are clean, concise and repeatable. Developers can create small blocks of codes that can then be called again without them having to rewrite the code or copy-paste the code over and over again. |
| 58 |
OOP says that bringing together data and its behaviour in a single location makes it easier to understand how a program works. FP says that data and behaviour are distinctively different things and should be kept separate for clarity. |
| 59 |
Functional programming is a programming paradigm, a style of building the structure and elements of computer programs, that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. |
| 60 |
Object-oriented languages are good when you have a fixed set of operations on things, and as your code evolves, you primarily add new things. This can be accomplished by adding new classes which implement existing methods, and the existing classes are left alone. |
| 61 |
Functional languages are good when you have a fixed set of things, and as your code evolves, you primarily add new operations on existing things. This can be accomplished by adding new functions which compute with existing data types, and the existing functions are left alone. |
| 62 |
Threading enables your C# program to perform concurrent processing so you can do more than one operation at a time. For example, you can use threading to monitor input from the user, perform background tasks, and handle simultaneous streams of input. |
| 63 |
As you've already learned, objects define their interaction with the outside world through the methods that they expose. Methods form the object's interface with the outside world; the buttons on the front of your television set, for example, are the interface between you and the electrical wiring on the other side of its plastic casing. You press the "power" button to turn the television on and off. |
| 64 |
Pluggability and debugging ease: If a particular object turns out to be problematic, you can simply remove it from your application and plug in a different object as its replacement. This is analogous to fixing mechanical problems in the real world. If a bolt breaks, you replace it, not the entire machine. |
| 65 |
Code re-use: If an object already exists (perhaps written by another software developer), you can use that object in your program. This allows specialists to implement, test and debug complex, task-specific objects, which you can then trust to run in your own code. |
| 66 |
Modularity: The source code for an object can be written and maintained independently of the source code for other objects. Once created, an object can be easily passed around inside the system. |
| 67 |
Software objects are conceptually similar to real-world objects: they too consist of state and related behavior. An object stores its state in fields (variables in some programming languages) and exposes its behavior through methods (functions in some programming languages). Methods operate on an object's internal state and serve as the primary mechanism for object-to-object communication. |
| 68 |
Objects are key to understanding object-oriented technology. Look around right now and you'll find many examples of real-world objects: your dog, your desk, your television set, your bicycle. |
| 69 |
A package is a namespace for organizing classes and interfaces in a logical manner. Placing your code into packages makes large software projects easier to manage. This section explains why this is useful, and introduces you to the Application Programming Interface (API) provided by the Java platform. |
| 70 |
A class is a blueprint or prototype from which objects are created. This section defines a class that models the state and behavior of a real-world object. It intentionally focuses on the basics, showing how even a simple class can cleanly model state and behavior. |
| 71 |
An interface is a contract between a class and the outside world. When a class implements an interface, it promises to provide the behavior published by that interface. This section defines a simple interface and explains the necessary changes for any class that implements it. |
| 72 |
Inheritance provides a powerful and natural mechanism for organizing and structuring your software. This section explains how classes inherit state and behavior from their superclasses, and explains how to derive one class from another using the simple syntax provided by the Java programming language. |
| 73 |
An object is a software bundle of related state and behavior. Software objects are often used to model the real-world objects that you find in everyday life. This lesson explains how state and behavior are represented within an object, introduces the concept of data encapsulation, and explains the benefits of designing your software in this manner. |
| 74 |
Of course, you can also create custom generic types and methods to provide your own generalized solutions and design patterns that are type-safe and efficient. The following code example shows a simple generic linked-list class for demonstration purposes. |
| 75 |
Although perfectly legal and sometimes intentional if you are creating a heterogeneous collection, combining strings and ints in a single ArrayList is more likely to be a programming error, and this error will not be detected until runtime. |
| 76 |
Generics provide the solution to a limitation in earlier versions of the common language runtime and the C# language in which generalization is accomplished by casting types to and from the universal base type Object. By creating a generic class, you can create a collection that is type-safe at compile-time. |
| 77 |
The limitations of using non-generic collection classes can be demonstrated by writing a short program that makes use of the ArrayList collection class from the .NET Framework base class library. ArrayList is a highly convenient collection class that can be used without modification to store any reference or value type. |
| 78 |
We could surround every unsafe area with a try - catch block, or we could create a separate "container" for every data type we need just to avoid casting. While both ways could work (and worked for many years), it is unnecessary now, because generics offers a much more elegant solution. |
| 79 |
Additionally, if the original data type we have chosen is a value type, such as int, we will incur a performance penalty every time we access the elements of the collection due to the autoboxing feature of C#. |
| 80 |
There are cases when you need to create a class to manage objects of some type, without modifying them. Without generics, the usual approach (highly simplified) to make such class would be like this. |
| 81 |
The most common use of generics is to create collection classes. Generic types were introduced to maximize code reuse, type safety, and performance. |
| 82 |
Generics are a new feature available since version 2.0 of the C# language and the common language runtime (CLR). Generics introduce to the .NET Framework the concept of type parameters, which make it possible to design classes and methods that defer the specification of one or more types until the class or method is declared and instantiated by client code. |
| 83 |
A derived class does not automatically inherit the base class' constructors, and it cannot be instantiated unless it provides its own. A derived class must call one of its base class' constructors by using the base keyword. |
| 84 |
If a base class contains a virtual method that it calls elsewhere and a derived class overrides that virtual method, the base class will actually call the derived class' method. Command line arguments are values that are passed to a console program before execution. For example, the Windows command prompt includes a copy command that takes two command line arguments. |
| 85 |
Structures need constructors - or better to say initialisers, as they do not construct but just initialise the memory - so that their contents are not left uninitialised. Therefore, constructors without parametres are not allowed. |
| 86 |
The principal difference between structs and classes is that instances of structs are values whereas instances of classes are references. Thus when you pass a struct to a function by value you get a copy of the object so changes to it are not reflected in the original because there are now two distinct objects but if you pass an instance of a class by reference then there is only one instance. |
| 87 |
Structures, or structs, are defined with the struct keyword followed by an identifier to name the structure. They are similar to classes, but have subtle differences. Structs are used as lightweight versions of classes that can help reduce memory management efforts when working with small data structures. |
| 88 |
The C# keyword value contains the value assigned to the property. After a property is defined it can be used like a variable. If you were to write some additional code in the get and set portions of the property it would work like a method and allow you to manipulate the data before it is read or written to the variable. |
| 89 |
C# properties are class members that expose functionality of methods using the syntax of fields. They simplify the syntax of calling traditional get and set methods (a.k.a. accessor methods). Like methods, they can be static or instance. |
| 90 |
The opposite of constructors, finalizers define the final behavior of an object and execute when the object is no longer in use. Although they are often used in C++ to free resources reserved by an object, they are less frequently used in C# due to the .NET Framework Garbage Collector. |
| 91 |
An object's finalizer, which takes no parameters, is called sometime after an object is no longer referenced, but the complexities of garbage collection make the specific timing of finalizers uncertain. |
| 92 |
A class's constructors control its initialization. A constructor's code executes to initialize an instance of the class when a program requests a new object of the class's type. Constructors often set properties of their classes, but they are not restricted to doing so. |
| 93 |
C# methods are class members containing code. They may have a return value and a list of parameters, as well as a generic type declaration. Like fields, methods can be static (associated with and accessed through the class) or instance (associated with and accessed through an object instance of the class methods as well as a generic type declaration. |
| 94 |
Classes are defined using the keyword class followed by an identifier to name the class. Instances of the class can then be created with the new keyword followed by the name of the class. |
| 95 |
The code below defines a class called Employee with properties Name and Age and with empty methods GetPayCheck() and Work(). It also defines a Sample class that instantiates and uses the Employee class. |
| 96 |
C# classes support information hiding by encapsulating functionality in properties and methods and by enabling several types of polymorphism, including subtyping polymorphism via inheritance and parametric polymorphism via generics. |
| 97 |
As in other object-oriented programming languages, the functionality of a C# program is implemented in one or more classes. The methods and properties of a class contain the code that defines how the class behaves. |
| 98 |
Follow class naming conventions, but start the name with I and capitalize the letter following the I. Example: IFoo The I prefix helps to differentiate between Interfaces and classes and also to avoid name collisions. |
| 99 |
If an assembly contains only one namespace, the assembly and the namespace should use the same name. Otherwise, assemblies should follow the normal Pascal Case format. There are no static methods within an interface, but any static methods can be implemented in a class that manages objects using it. In addition to methods and properties, interfaces can declare events and indexers as well. |
| 100 |
A convention used in the .NET Framework (and likewise by many C# programmers) is to place an "I" at the beginning of an interface name to distinguish it from a class name. Another common interface naming convention is used when an interface declares only one key method. |
| 101 |
Although a class can inherit from one class only, it can inherit from any number of interfaces. This is a simplified form of multiple inheritance supported by C#. When inheriting from a class and one or more interfaces, the base class should be provided first in the inheritance list, followed by any interfaces to be implemented. |
| 102 |
An interface in C# is a type definition similar to a class, except that it purely represents a contract between an object and its user. It can neither be directly instantiated as an object, nor can data members be defined. So, an interface is nothing but a collection of method and property declarations. |
| 103 |
Casting is a way to convert values from one type to another. Mainly, two types of casting exist, Implicit casting and Explicit casting. Boxing occurs when a value type is cast to an object, or reference type. |
| 104 |
Implicit casting is the way values are cast automatically by the compiler. This happens if and only if no loss of information occurs. Examples can be seen when converting data from smaller integral types to larger types, or derived types to the base type. |
| 105 |
When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class. However, if it does not, then the subclass must also be declared abstract. |
| 106 |
A second difference is that an abstract class may have abstract members. As was shown above, this is not a must. To create a class with at least one abstract member, the abstract keyword must be added before the class keyword. |
| 107 |
An abstract class can only be subclassed; it cannot be instantiated. An abstract class can contain abstract methods—methods that are declared but not implemented. Subclasses then provide the implementations for the abstract methods. |
| 108 |
Except for the Object class, a class has exactly one direct superclass. A class inherits fields and methods from all its superclasses, whether direct or indirect. A subclass can override methods that it inherits, or it can hide fields or methods that it inherits. (Note that hiding fields is generally bad programming practice.) |
| 109 |
You can prevent a class from being subclassed by using the final keyword in the class's declaration. Similarly, you can prevent a method from being overridden by subclasses by declaring it as a final method. |
| 110 |
An abstract class is somewhere between a C# interface and a non-abstract class. Of the public members defined by an abstract class, any number of those members may include an implementation. |
| 111 |
In C#, it is possible to have a type that is intermediate between a pure interface that does not define any implementation, and a type that defines a complete implementation. This is called an abstract class and is defined by including the abstract keyword in the class definition. |
| 112 |
Abstract classes are similar to interfaces. You cannot instantiate them, and they may contain a mix of methods declared with or without an implementation. However, with abstract classes, you can declare fields that are not static and final, and define public, protected, and private concrete methods. |
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