Govt. Exams
Entrance Exams
Abstract classes in C# cannot be instantiated directly. The compiler enforces this rule at compile-time. Abstract classes serve as blueprints and must be inherited by concrete classes that provide implementations for all abstract members. This ensures proper design and forces derived classes to implement required functionality.
Abstract methods have no implementation in the abstract class and force derived classes to provide their own implementation. They cannot be private as they must be overridable.
Interfaces in C# define a set of method and property declarations that implementing classes must provide, establishing a contract without implementation details.
The four pillars of OOP are Inheritance, Polymorphism, Encapsulation, and Abstraction. Compilation is a language feature, not an OOP principle.
C# uses colon (:) to implement interfaces, and multiple interfaces are separated by commas. The 'implements' keyword is used in Java, not C#.
The 'abstract' keyword prevents instantiation of a class and forces derived classes to implement abstract members, establishing a contract for subclasses.
Encapsulation bundles data and methods together, hiding internal implementation and controlling access through public interfaces, improving maintainability and security.
'this' keyword represents the current instance of the class. It is used to access instance members, differentiate between local and instance variables, and pass the current object as a parameter.
public class Employee
{
private string name = "John";
public Employee(string n) { name = n; }
}
Employee emp = new Employee("Alice");
Console.WriteLine(emp.name);
The 'name' field is declared as 'private', so it cannot be accessed outside the class. Attempting to access emp.name from outside the class results in a compilation error.
The 'base' keyword allows a derived class to access members (methods, properties, constructors) of the parent class. It's commonly used to call the parent constructor or override methods while keeping parent functionality.
