Encapsulation is defined as the wrapping up of data under a single unit. It is the mechanism that binds together code and the data it manipulates. In a different way, encapsulation is a protective shield that prevents the data from being accessed by the code outside this shield.

Technically in encapsulation, the variables or data of a class are hidden from any other class and can be accessed only through any member function of own class in which they are declared. Encapsulation can be achieved by declaring all the variables in the class as private and writing public methods in the class to set and get the values of variables.

# Crystal program to illustrate encapsulation 

    class Demoencapsulation 
    @id : Int32
        @name : String
        @addr : String
def initialize(id, name, addr) 

# Instance Variables     
@id  = id 
@name  = name 
@addr  = addr 
end

# displaying result 
def display_details() 
    puts "Customer id: #{@id}"
    puts "Customer name: #{@name}"
    puts "Customer address: #{@addr}"
end
end

# Create Objects 
cust1 = Demoencapsulation .new  1, "xx", "xyy"
cust2 = Demoencapsulation.new   2, "aa", "aabb"


# Call Methods 
cust1.display_details()
cust2.display_details()

Output

Customer id: 1

Customer name: xx

Customer address: xyy

Customer id: 2

Customer name: aa

Customer address: aabb

Explanation: In the above program, the class Demoencapsulation encapsulate the methods of the class. You can only access these methods with the help of objects of the Demoencapsulation class i.e. cust1 and cust2.

Advantages of Encapsulation:

Data Hiding:The user will have no idea about the inner implementation of the class. It will not be visible to the user that how the class is storing values in the variables. User only knows that we are passing the values to a setter method and variables are getting initialized with that value. Re usability: Encapsulation also improves the re-usability and easy to change with new requirements. Testing code is easy:Encapsulated code is easy to test for unit testing.

source :geeksforgeeks