Encapsulation and Access Modifiers

  • Encapsulation and Access Modifiers

What do we understand by the word “encapsulation”? It is a mechanism to bind something together and keep it safe from outside interference and misuse.

In programming, encapsulation is used to refer to one of two related but distinct notions, and sometimes to the combination thereof:

  • A language mechanism for restricting direct access to some of the object’s components.
  • A language construct that facilitates the bundling of data with the methods (or other functions) operating on that data.

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In simple words, if you want to limit the access of any classes or methods or variables, you can use encapsulation.

In Dart, encapsulation is done by using the keywords public, private and protected.

Modifier Description
public The default, visible everywhere
private Visible only in the the current classes or files based on the scenerio

Dart doesn’t have a protected keyword, but it does have a concept of libraries that can help you achieve the same effect.

Public Access Modifier

If you don’t specify any modifier, it is by default public.


class Person {
  String name;
  int age;
}

Private Access Modifier

If you want to make any class, method or variable private, you can use the underscore _ symbol.


class Person {
  String _name;
  int _age;
}

Defining private and public varibles

Public Varibales

Public varibales are those which are accessible from anywhere in the program or project. We need the import (path) of the file and that will be accessible.

int age = 10;  

String name = "John Doe";

Private Varibales

Private varibales are those which are accessible only from the same file. We can’t access them from other files.

int _age = 10;

String _name = "John Doe";

Note that, if you try to access the private varibales from other files, you will get an error.

Note:

If we can’t access the private varibales, why create them? Well, they are useful in many ways.

  • If you want to use a variable only in a single file, you can make it private.
  • If you want to use a variable only in a single class, you can make it private.
  • If you want to use a variable only in a single method, you can make it private.

Other than that, you can use private varibales to make your code more readable and optimized by hiding the implementation details.

We can access the private variables with getters and setters.

Getters and Setters in Dart

We learned about the encapsulation which limits the access of variables and methods from outside the class. But sometimes we need to access the private variables from outside the class. In this case, we use getters and setters.

Getters and setters are special methods that provide read and write access to an object’s properties.

Why do we need getters and setters ?

Getters and setters are used to protect your data, particularly when creating classes. For each instance variable, a getter method returns its value while a setter method sets or updates its value.

How to create getters and setters ?

To create a getter and setter, we use the get and set keywords. Rules for creating getters and setters are as follows:

  • Getters and setters must have the same name as the instance variable.
  • The setter method must have a single parameter and no return type.
  • The getter method must have no parameters and return a value.

Now, following the above rules, let’s create a getter and setter for a class.


class Student {
  String name;
  int age;

  String get studentName {
    return name;
  }

  void set studentName(String name) {
    this.name = name;
  }

  int get studentAge {
    return age;
  }

  void set studentAge(int age) {
    this.age = age;
  }
}

void main() {
  var student = Student();
  student.studentName = 'Peter';
  student.studentAge = 20;
  print(student.studentName);
  print(student.studentAge);
}

Output

Peter
20

In the above example, we have created a class named Student. The class has two instance variables name and age. We have created getters and setters for these variables.

Note that, setters is not a function here it is a varibale that takes a value and assigns it to the instance variable.

Shorthand syntax for getters and setters

Dart provides a shorthand syntax for getters and setters.


class Student {
  String name;
  int age;

  String get studentName => name;

  void set studentName(String name) => this.name = name;

  int get studentAge => age;

  void set studentAge(int age) => this.age = age;
} 

void main () {
  var student = Student();
  student.studentName = 'Peter';
  student.studentAge = 20;
  print(student.studentName);
  print(student.studentAge);
}

Output

Peter
20

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