Interview Questions and Answers

Encapsulation is the bundling of data and methods that operate on that data into a single unit known as a class. It restricts access to some of the object's components.

Polymorphism allows objects of different types to be treated as objects of a common type. It can take the form of method overloading or method overriding.

Method overloading is a feature in OOP where a class can have multiple methods with the same name but with different parameter types or a different number of parameters.

Example:

class MathOperations {
  add(a, b) {
    return a + b;
  }
  add(a, b, c) {
    return a + b + c;
  }
}

An interface in OOP defines a contract for classes, specifying a set of methods that a class must implement. It allows for achieving multiple inheritance in languages that don't support it directly.

Example:

interface Printable {
  print();
}

Method overriding occurs when a subclass provides a specific implementation for a method that is already defined in its superclass. It allows a subclass to provide a specialized version of a method.

Example:

class Animal {
  speak() {
    console.log('Animal speaks');
  }
}
class Dog extends Animal {
  speak() {
    console.log('Dog barks');
  }
}

A destructor is a method that is called when an object is about to be destroyed. In many programming languages, like C++, it is used to release resources held by the object.

Example:

class MyClass {
  destructor() {
    // clean up resources
  }
}

A virtual function is a function in a base class that is declared using the 'virtual' keyword and can be overridden by a derived class. It enables dynamic method binding and polymorphism.

Example:

class Shape {
  virtual calculateArea() = 0;
}

An abstract method is a method declared in an abstract class or an interface that has no implementation in the base class. Subclasses must provide an implementation for abstract methods.

Example:

abstract class Printer {
  abstract print();
}

Constructor chaining refers to the process of calling one constructor from another in the same class or a superclass. It allows for reusing code and initializing objects more efficiently.

Example:

class Vehicle {
  constructor(make) {
    this.make = make;
  }
}
class Car extends Vehicle {
  constructor(make, model) {
    super(make);
    this.model = model;
  }
}

In OOP, the 'final' keyword can be applied to classes, methods, or variables. It indicates that a class cannot be extended, a method cannot be overridden, or a variable cannot be reassigned.

Example:

final class MyFinalClass {
  // class content
}

Method hiding occurs when a subclass provides a static method with the same signature as a static method in its superclass. It does not override the method but hides it.

Example:

class Parent {
  static show() {
    console.log('Static method in Parent');
  }
}
class Child extends Parent {
  static show() {
    console.log('Static method in Child');
  }
}

In C#, an abstract class is a class that cannot be instantiated and may contain abstract methods. It is used to provide a common base for related classes and enforce a certain structure on derived classes.

Example:

abstract class Shape {
  public abstract void Draw();
}

'is-a' relationship represents inheritance, where a class is a specialized version of another class. 'has-a' relationship represents composition, where a class contains an instance of another class as a member.