What is an Object?
An object is an instance of a class. It can be uniquely identified by its name and it defines a state which is represented by the values of its attributes at a particular time.
An object can be considered a "thing" that can perform a set of activities. The set of activities that the object performs defines the object's behavior.
The state of the object changes according to the methods which are applied to it. We refer to these possible sequences of state changes as the behavior of the object. So the behavior of an object is defined by the set of methods which can be applied on it.
Objects can communicate by passing messages to each other.
What is inheritance?
Inheritance is the mechanism which allows a class A to inherit properties of a class B. We say "A inherits from B''. Objects of class A thus have access to attributes and methods of class B without the need to redefine them.
If class A inherits from class B, then B is called superclass of A. A is called subclass of B. Objects of a subclass can be used where objects of the corresponding superclass are expected. This is due to the fact that objects of the subclass share the same behavior as objects of the superclass.
However, subclasses are not limited to the state and behaviors provided to them by their superclass. Subclasses can add variables and methods to the ones they inherit from the superclass.
In the literature you may also find other terms for "superclass" and "subclass". Superclasses are also called parent classes or base classes. Subclasses may also be called child classes or just derived classes.
Inheritance Example
Like a car, truck or motorcycles have certain common characteristics- they all have wheels, engines and brakes. Hence they all could be represented by a common class Vehicle which encompasses all those attributes and methods that are common to all types of vehicles.
However they each have their own unique attributes; car has 4 wheels and is smaller is size to a truck; whereas a motorcycle has 2 wheels. Thus we see a parent-child type of relationship here where the Car, Truck or Motorcycle can inherit certain Characteristics from the parent Vehicle; at the same time having their own unique attributes. This forms the basis of inheritance; Vehicle is the Parent, Super or the Base class. Car, Truck and Motorcycle become the Child, Sub or the Derived class.
What is a Virtual Functions in class?
A virtual function is a member function of the base class and which is redefined by the derived class. When a derived class inherits the class containing the virtual function, it has ability to redefine the virtual functions.
A virtual function has a different functionality in the derived class according to the requirement. The virtual function within the base class provides the form of the interface to the function. Virtual function implements the philosophy of one interface and multiple methods (polymorphism).
The virtual functions are resolved at the run time. This is called dynamic binding. The functions which are not virtual are resolved at compile time which is called static binding. A virtual function is created using the keyword virtual which precedes the name of the function.
What is Encapsulation in Object Oriented Programming (OOPS) Languages?
Encapsulation is the procedure of covering up of data and functions into a single unit. Encapsulation (also information hiding) consists of separating the external aspects of an object which are accessible to other objects, from the internal implementation details of the object, which are hidden from other objects.
A process, encapsulation means the act of enclosing one or more items within a (physical or logical) container (Class).
Object-oriented programming is based on encapsulation. When an objects state and behavior are kept together, they are encapsulated. That is, the data that represents the state of the object and the methods (Functions and Subs) that manipulate that data are stored together as a cohesive unit.
The object takes requests from other client objects, but does not expose its the details of its data or code to them. The object alone is responsible for its own state, exposing public messages for clients, and declaring private methods that make up its implementation. The client depends on the (hopefully) simple public interface, and does not know about or depend on the details of the implementation.
For example, a HashTable object will take get() and set() requests from other objects, but does not expose its internal hash table data structures or the code strategies that it uses.
Explain the advantages of Encapsulation in Object Oriented Programming Languages.
Benefits of Encapsulation in oops: Encapsulation makes it possible to separate an objects implementation from its behavior to restrict access to its internal data. This restriction allows certain details of an objects behavior to be hidden. It allows us to create a "black box" and protects an objects internal state from corruption by its clients.
Encapsulation is a technique for minimizing interdependencies among modules by defining a strict external interface. This way, internal coding can be changed without affecting the interface, so long as the new implementation supports the same (or upwards compatible) external interface. So encapsulation prevents a program from becoming so interdependent that a small change has massive ripple effects.
The implementation of an object can be changed without affecting the application that uses it for: Improving performance, fix a bug, consolidate code or for porting.
Limitations and Restrictions of Interface
The essential idea to remember is that an interface never contains any implementation. The following restrictions and imitations are natural consequences of this:
You're not allowed any fields in an interface, not even static ones. A field is an implementation of an object attribute.
You're not allowed any constructors in an interface. A constructor contains the statements used to initialize the fields in an object, and an interface does not contain any fields!
You're not allowed a destructor in an interface. A destructor contains the statements used to destroy an object instance.
You cannot supply an access modifier. All methods in an interface are implicitly public.
You cannot nest any types (enums, structs, classes, interfaces, or delegates) inside an interface.
What is the difference between abstract class and interface?
We use abstract class and interface where two or more entities do same type of work but in different ways. Means the way of functioning is not clear while defining abstract class or interface. When functionality of each task is not clear then we define interface. If functionality of some task is clear to us but there exist some functions whose functionality differs object by object then we declare abstract class.
We can not make instance of Abstract Class as well as Interface. They only allow other classes to inherit from them. And abstract functions must be overridden by the implemented classes. Here are some differences in abstract class and interface.
An interface cannot provide code of any method or property, just the signature. We dont need to put abstract and public keyword. All the methods and properties defined in Interface are by default public and abstract. An abstract class can provide complete code of methods but there must exist a method or property without body.
A class can implement several interfaces but can inherit only one abstract class. Means multiple inheritance is possible in .Net through Interfaces.
What is a static class?
We can declare a static class. We use static class when there is no data or behavior in the class that depends on object identity. A static class can have only static members. We can not create instances of a static class using the new keyword. .NET Framework common language runtime (CLR) loads Static classes automatically when the program or namespace containing the class is loaded.
Here are some more features of static class:
- Static classes only contain static members.
- Static classes can not be instantiated. They cannot contain Instance Constructors
- Static classes are sealed.
What is static member of class?
A static member belongs to the class rather than to the instances of the class. In C# data fields, member functions, properties and events can be declared static. When any instances of the class are created, they cannot be used to access the static member.
To access a static class member, use the name of the class instead of an instance variable
Static methods and Static properties can only access static fields and static events.
Like: int i = Car.GetWheels;
Here Car is class name and GetWheels is static property.
Static members are often used to represent data or calculations that do not change in response to object state.
What is the difference between value parameter and reference parameter?
A value parameter is used for "in" parameter passing, in which the value of an argument is passed into a method, and modifications of the parameter do not impact the original argument. A value parameter refers to its own variable, one that is distinct from the corresponding argument. This variable is initialized by copying the value of the corresponding argument.
A reference parameter is used for "by reference" parameter passing, in which the parameter acts as an alias for a caller-provided argument. A reference parameter does not itself define a variable, but rather refers to the variable of the corresponding argument. Modifications of a reference parameter impact the corresponding argument.
What is the use of parameter array?
A parameter array enables a many-to-one relationship: many arguments can be represented by a single parameter array. In other words, parameter arrays enable variable length argument lists.
A parameter array is declared with a params modifier in C#. There can be only one parameter array for a given method, and it must always be the last parameter specified. The type of a parameter array is always a single dimensional array type. A caller can either pass a single argument of this array type, or any number of arguments of the element type of this array type.
What is a constant?
A constant is a class member that represents a constant value: a value that can be computed at compile-time.
Constants are permitted to depend on other constants within the same program as long as there are no circular dependencies. The example
class Constants {
public const int A = 1;
public const int B = A + 1;
}
shows a class named Constants that has two public constants.
Happy Programming!!!