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Encapsulation

This lesson shows us how to implement the first component of data hiding: encapsulation.

We'll cover the following...

A Real Life Example

For the sake of explanation, we’ll start off by creating a simple movie class which contains three members:

C++
class Movie{
  string title;
  int year;
  string genre;
  public:
  Movie(){
    title = "";
    year = -1;
    genre = "";
  }
  Movie(string t, int y, string g){
    title = t;
    year = y;
    genre = g;
  }
};

There must be a way to interact with the title, year and genre variables. They hold all the information about a movie, but how do we access or modify them?

We could create a getTitle() method which would return the title to us. Similarly, the other two members could also have corresponding get functions.

By observing the emerging pattern, we can make a definitive conclusion. These functions should be part of the class of itself! Let’s try it out.

C++
#include <iostream>
#include <string>
using namespace std;
class Movie{
  string title;
  int year;
  string genre;
  public:
  Movie(){
    title = "";
    year = -1;
    genre = "";
  }
  Movie(string t, int y, string g){
    title = t;
    year = y;
    genre = g;
  }
  
  string getTitle(){
    return title;
  }
  void setTitle(string t){
    title = t;
  }
  
  int getYear(){
    return year;
  }
  void setYear(int y){
    year = y;
  }
  
  string getGenre(){
    return genre;
  }
  void setGenre(string g){
    genre = g;
  }
  
  void printDetails(){
    cout << "Title: " << title << endl;
    cout << "Year: " << year << endl;
    cout << "Genre: " << genre << endl;
  }
};
int main() {
  Movie m("The Lion King", 1994, "Adventure");
  m.printDetails();
  
  cout << "---" << endl;
  m.setTitle("Forrest Gump");
  cout << "New title: " << m.getTitle() << endl;
}

We have now provided an interface of public methods to interact with the Movie class. Our private variables cannot be accessed directly from the outside, but we have provided read and write functions which allow access those variables.

This, in essence, is data encapsulation.

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Advantages of Encapsulation

  • Classes are easier to change and maintain.
  • We can specify which data member we want to keep hidden or accessible.
  • We decide which variables have read/write privileges (increases flexibility).

In the next lesson, we’ll discuss the second component of data hiding: abstraction.