Hi
Today,
we will be looking at the most important and favorite topic of OOP i.e.
encapsulation.
To
explain the concept of encapsulation We will be using the java examples this
concept remains same for any Object Oriented programming language.
First
of all let’s look at the meaning of encapsulation. Encapsulation means to
enclose something or we can say to cover something protectively.
When
we read the above statement few questions arises
1. Why should we protect
/hide something?
2. What we need to
protect?
3. What happens if we
don’t protect?
With
below example let us try to answer these questions
The
state of an Object depends on the data stored in variable, which means to say
in order to save the state of any object we need to protect the our variables’.We
need to protect all those variable which can change the state of the object. The
concept of protecting or ensuring the safety of our variable is called
encapsulation
package com.alwaysJava.encapsulation;
public class UnderstandingEncapsulation
{
public int
numberOfStudentsEnroled;
public final
int maxNumberOfStudents=100;
public int
getNumberOfStudents()
{
return numberOfStudentsEnroled;
}
}
package com.alwaysJava.encapsulation;
public class DriverClass
{
public static
void main(String[] args)
{
UnderstandingEncapsulation uE=new UnderstandingEncapsulation();
uE.numberOfStudentsEnroled=10;
System.out.println(uE.getNumberOfStudents());
}
}
By
running the above output we will see the output to be 10.
We
may feel at first look that the code is working really fine why we need to
encapsulate?
If we
observe carefully we will know that we are giving too much power to the DriverClass,
which allows user to even set negative values to numberOfStudentsEnroled
as -100, or set 65535 as the number of students enrolled against maximum
capacity of 100.
So
how can we protect out class from being exploited by user, in order to do this
we need to validate the input given by the user, this can be achieved by
providing setter and getter methods and also by setting access specifier as
private
package com.alwaysJava.encapsulation;
public class UnderstandingEncapsulation
{
private int
numberOfStudentsEnroled;
public final
int maxNumberOfStudents=100;
public int
getNumberOfStudents()
{
return numberOfStudentsEnroled;
}
public void
setNumberOfStudents(int userInput)
{
if(userInput>maxNumberOfStudents)
throw new IllegalArgumentException();
else
numberOfStudentsEnroled=userInput;
}
}
By
changing the UnderstandingEncapsulation class variables to private we can force
the user to set a correct value, if the user tries to set an invalid value we
can throw a illegalArgumentException which is an uncheck exception, by doing
this we protect our code from taking illegal values and hence protecting
functionality of the code.
This
concept of protecting the code from user is called encapsulation.
Hence
by using the right coding practices and concepts we give the programmers more
power to change the code at a later stage when required without making any
changes to the code or implementation of the class.
It is industry best practice to have a validate method
in every class, whenever there is a possibility of change in object we need to
invoke this method to check the value set to instances are correct by doing so
it helps to identify bugs at a very early stage and the debugging will be
comparatively easier.
