Encapsulation in Java or object oriented programming language is a concept which enforces protecting variables, functions from outside of class, in order to better manage that piece of code and having least impact or no impact on other parts of a program due to change in protected code. Encapsulation in Java is visible at different places and Java language itself provide many constructs to encapsulate members. You can completely encapsulate a member be it a variable or method in Java by using private keyword and you can even achieve a lesser degree of encapsulation in Java by using other access modifiers like protected or the public. The true value of encapsulation is realized in an environment which is prone to change a lot and we know that in software requirements changes every day at that time if you have your code well encapsulated you can better manage risk with a change in requirement. Along with abstraction in java and polymorphism in Java, Encapsulation is a must know the concept. In this java tutorial, we will see How to use encapsulation in Java, advantage and disadvantage of Encapsulation and various design patterns and real life problems which make use of Encapsulation object oriented concept. If you are looking for a quick guide on both OOPS and SOLID design principle in Java then you may find 10 Object Oriented Design principles Java programmer should know interesting.
What is Encapsulation in Java

Since this code is not well encapsulated i.e. not confined in one place you need to change everywhere you are calling this constructor i.e. for one change you need to modify several file instead of just one file which is more error prone and tedious, though it can be done with refactoring feature of advanced IDE wouldn't it be better if you only need to make change at one place? Yes, that is possible if we encapsulate Loan creation logic in one method say createLoan() and client code call this method and this method internally create Loan object. in this case, you only need to modify this method instead of all client code.
Example of Encapsulation in Java
class Loan{
private int duration; //private variables examples of encapsulation
private String loan;
private String borrower;
private String salary;
private int duration; //private variables examples of encapsulation
private String loan;
private String borrower;
private String salary;
//public constructor can break encapsulation instead use factory method
private Loan(int duration, String loan, String borrower, String salary){
this.duration = duration;
this.loan = loan;
this.borrower = borrower;
this.salary = salary;
}
private Loan(int duration, String loan, String borrower, String salary){
this.duration = duration;
this.loan = loan;
this.borrower = borrower;
this.salary = salary;
}
//no argument constructor omitted here
// create loan can encapsulate loan creation logic
public Loan createLoan(String loanType){
//processing based on loan type and then returning loan object
//processing based on loan type and then returning loan object
return loan;
}
}
In this same example of Encapsulation in Java, you see all member variables are made private so they are well encapsulated you can only change or access this variable directly inside this class. if you want to allow outside world to access these variables is better creating a getter and setter e.g. getLoan() that allows you to do any kind of validation, security check before return loan so it gives you complete control of whatever you want to do and single channel of access for client which is controlled and managed.
Advantage of Encapsulation in Java and OOPS
Here are few advantages of using Encapsulation while writing code in Java or any Object oriented programming language:
1. Encapsulated Code is more flexible and easy to change with new requirements.
2. Encapsulation in Java makes unit testing easy.
3. Encapsulation in Java allows you to control who can access what.
4. Encapsulation also helps to write immutable class in Java which is a good choice in multi-threading
environment.
5. Encapsulation reduces coupling of modules and increases cohesion inside a module because all piece of one thing
is encapsulated in one place.
6. Encapsulation allows you to change one part of code without affecting other parts of code.
What should you encapsulate in code
Anything which can be change and more likely to change in near future is a candidate of Encapsulation. This also helps to write more specific and cohesive code. An example of this is object creation code, code which can be improved in future like sorting and searching logic.
Design Pattern based on Encapsulation in Java
Many design pattern in Java uses encapsulation concept, one of them is Factory pattern which is used to create objects. Factory pattern is a better choice than new operator for creating an object of those classes whose creation logic can vary and also for creating different implementation of the same interface. BorderFactory class of JDK is a good example of encapsulation in Java which creates different types of Border and encapsulate creation logic of Border. Singleton pattern in Java also encapsulate how you create an instance by providing getInstance() method. since an object
is created inside one class and not from any other place in code you can easily change how you create an object without
affect another part of code.
Important points about encapsulation in Java.
1. "Whatever changes encapsulate it" is a famous design principle.
2. Encapsulation helps in loose coupling and high cohesion of code.
3. Encapsulation in Java is achieved using access modifier private, protected and public.
4. Factory pattern , Singleton pattern in Java makes good use of Encapsulation.
Further Learning
SOLID Principles of Object Oriented Design
Absolute Introduction to Object Oriented Programming in Java
Java - Object Oriented Programming [For Absolute Beginners]
Other Java design pattern articles you may like :
16 comments :
Nice Explanation Javin. Clear & Crisp...
For my Take on Encapsulation - Click Here
Anand
Very well said.
In short, from OOAD perspective:
- Abstraction is about 'What' a class can do.
- Encapsulation is more about 'How' to achieve that functionality.
Since it is not required to reveal the information of 'How'(trade/business secrets) the class achieves a functionality - hence we wrap it with private and protected scope based on need.
-Pankaj
well said Pankaj, It will help to understand difference between Abstraction and Encapsulation
Does Data hiding and Encapsulation is same principle ? Some one ask me in OOPS Interview that What is data hiding and What is Encapsulation, I am getting confused is it two different concept or just one ?
Thanks for sharing. I would like to share few OOPS Interview questions which is based on concept of Encapsulation, Abstraction and Polymorphism in Java programming.
What is difference between Encapsulation and Abstraction in Java or OOPS ?
What is difference between Encapsulation vs Data hiding in Java?
Encapsulation vs Abstraction vs Data hiding vs Polymorphism
Difference between Encapsulation and Inheritnace in Java.
Encapsulation vs Inheritance vs Composition in Java
Can you give a real life Example of Encapsulation in Java which you have used in your Java project ?
how do make method and field encapsulated in Java programming language ?
honestly i don't get it,how we can create object in this example
consructor of class Loan has private modificator
we need static method that return new Loan(....)
@Anonymous, you are correct. Actually createLoan() was that static factory method which supposed to return Loan object, until now, when I realized it's missing static modifier :). Thanks for pointing it out.
Hello,
I am unable to get the differences between Object initialization through Parameterized constructor and the creatLoan() method from the explanation above. Both are doing the same job..
Suppose, If we want to add a new attribute to the class in future (borrower age as per the example), Its necessary to modify all the object creation codes in all the files. But how come this effort will be reduced in case of the creator methods?? (Because we are introducing an extra attribute in the class, we need it through some mechanism from the users(object creation requestor files). And that will ofcourse require extra modifications in files.,
Can you please clarify this...
Thanks.
(continuation of comment logged:June 11, 2013 at 1:45 AM )
For Example :
Code At Present:
Loanacc l = new Loanacc(ATT1,ATT2,ATT3); // Obj creation using parameterized constructors
Loanacc l = new Loanacc();
l.createLoan(ATT1,ATT2,ATT3); // obj creation using create() method
To add AGE in future, the above lines may be changed to,
Loanacc l = new Loanacc(ATT1,ATT2,ATT3,AGE);
Loanacc l = new Loanacc();
l.createLoan(ATT1,ATT2,ATT3,AGE);
So, this requires code change in all the files whichever has the above object creation code(no matter which method is used)..,
Am I missing some understanding here?
OOP is meant to be a programmer own secret jutsu, the stronger your jutsu is the easier you can defeat "Work" :-)
class Loanacc{
function createLoan($ATT1 = null ,$ATT2 = null,$ATT3 = null,$AGE = null){
echo "Hi i am " . $ATT1 " and my age is " . $AGE;
}
}
Loanaccl = new Loanacc()
Loanaccl->createLoan(firstname,middlename,lasname,15); // should output "Hi i am firstname and my age is 15
if we have public getter and setter then those variables becomes public ...so wats d use??
Gone through above loan creation example. My question is do we need to pass relevant parameters to createLoan method
ex : createLoan(int duration, String loan, String borrower, String salary) . if we not providing above parameter how can we create loan object dynamically. Then how can code flexibility happen, everywhere in application where createLoan method has no change ?
Dear Sir,What is the difference in creating a createloan method and using parameterized costructor,both ways we need to changw in all files where object is created...???????????????????
Very good questions . Here are some 30 Java OOP concept interview questions, I have found immensely useful. Thanks
Both are same
Your example description is a bit abstract please include some more points which are asked in questions above so that the readers wont have these kind of confusions in the future.
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