Top Java Encapsulation Interview Questions (2024)

1. What is Encapsulation in Java?

2. How Encapsulation is helpful in java?

3. What are the advantages of Encapsulation?

4. What are the difference between data hiding and Encapsulation?

5. Where Encapsulation is used?

6. What are the difference between Encapsulation and Inheritance?

7. What is the difference between Encapsulation and Abstraction?

8. Why Encapsulation is called Data hiding in Java?

9. What are the advantages of using Encapsulation?

10. How to achieve Encapsulation in Java with Example?

11. What is a tightly encapsulated class?

12. How does getter and setter functions help in encapsulation?

13. Is Encapsulation violating reflection?

14. Which design pattern is based on encapsulation in Java?

15. What is the difference between Encapsulation and Polymorphism?

Q: What is Encapsulation in Java?
Ans:

Encapsulation is the main concept of OOPs (Object-Oriented programming). Encapsulation means wrapping or binding data and methods in a single unit. It is also known as data hiding. Data hiding means it derived the result of a specific class. This also means that is not directly accessible. Data in Encapsulation is private, the results of the data are called by using different methods. The code is wrapped in such a way that it cannot be randomly accessed by other codes outside the class.

Encapsulation Rules:

1. Always make-instance variable private.
2. Always make public accessor methods and force calling code to these methods instead of directly calling the instance variable.
3. Use naming convention set() and get for these methods.

package encapsulation;

public class DebitCard {

    private int accountno = 789012;
    private int pinno = 6543;
    private double balanceamount = 200000;

    public void withdrawAmount(int accountno, int pinno; int amountwithdraw) {
       System.out.printIn("amountwithdraw < balanceamount")
    }
}

Q: How Encapsulation is helpful in Java?
Ans:

1. Encapsulated codes can be tested easily. Encapsulation helps in securing the code.
2. To do changes in the Encapsulated code is easy as we can change in a code or class without affecting other code or classes.
3. Encapsulated code can be reused and maintained for data hiding.

Q: What are the advantages of Encapsulation?
Ans:

1. Security: It keeps the codes and data safe from external inheritance.
2. Flexibility: It keeps the codes and data safe from external inheritance.
3. Easy unit testing: As all data is encapsulated or wrapped in a single unit the code testing becomes easier.
4. Reuse of code: It allows modifying implemented code without breaking other code that has implemented the code.

Q: What are the difference between data hiding and Encapsulation?
Ans:

Data hiding and encapsulation both are important concepts of object-oriented programming.

Data hiding means protecting the variable of a class from outside world access. Encapsulation means wrapping or binding data in a single unit.

The core differences between data hiding and encapsulation are :

Data hiding	Encapsulation
Data hiding more focuses on securing the data along with hiding.	Encapsulation focuses more on wrapping data to make classes and the methods in the simplest form for the system.
It is a technique and process both.	It is a sub-process in data hiding.
The data is always private and inaccessible.	The data may be private or public.

Q: Where Encapsulation is used?
Ans:

Encapsulation is used in various design patterns and real-life problems that make use of the Encapsulation object-oriented concept. It is used to hide the values or state of a structured data object inside a class, preventing unauthorized parties direct access to them.

Q: What are the difference between Encapsulation and Inheritance?
Ans:

Difference	Encapsulation	Inheritance
Basic	Encapsulation in Java is the process of enclosing variables and methods code that perform on data as a single unit. It hides a class's variables, helping to make them unreachable from outside the class.	Inheritance is the process of creating a new class by using an existing class in a function. In other words, inheritance is a process where a child class /subclass inherits all the properties and behaviors of the parent class/superclass.
Focus	It focuses on minimizing the complex system. It mainly works in Design patterns.	It focuses on behavior and attributes of a parent class is inherited by the child class.
Conclusion	The result is derived by calling a particular class without affecting other classes.	The result is derived by calling each class that is inherited.
Process	Encapsulation has methods in which there is one main class and other sub-classes (private, protected, public).	Types of inheritance are FIVE : Single Inheritance Multilevel Inheritance Hierarchical Inheritance Multiple Inheritance (Through Interface) Hybrid Inheritance (Through Interface)

Examples:

1. The classes can be added in Encapsulation by creating different packages.

   //Division of two numbers
   public class Division {
   
    public static void main(String[] args) {
     System.out.println(100/20);
    }
   
   }

2. The child classes are added in inheritance by adding "extends" in classes.

   class Card {
       void cardDetails() {
           System.out.println("Card Details...");
       }
   }
   
   class CreditCard extends Card {
       void creditCardDetails() {
           System.out.println("Credit Card Details...");
       }
   }
   
   public class Bank {
       public static void main(String args[]) {
           CreditCard card = new CreditCard();
           card.cardDetails();
           card.creditCardDetails();
       }
   }

   Output:

   "C:\Program Files\Java\jdk-12.0.2\bin\java.exe"  ...
   Card Details...
   Credit Card Details...

Q: What is the difference between Encapsulation and Abstraction?
Ans:

1. Definition: Encapsulation is wrapping or binding data in a single unit.
2. Abstraction is hiding the implementation details from the user.
3. Encapsulation solves the problem at an implementation level. Abstraction solves the problem at a design level.
4. Encapsulation is used for code binding in single-unit to protect from the outside world.
5. Abstraction is used for hiding unwanted data and giving results for relevant data.
6. Encapsulation focus on an object, its behavior and properties, and what it does.
7. Abstraction only focuses on the object and not how it works.
8. Example of Encapsulation: Laptop: Inner implementation of the laptop, display screen, and buttons are connected using different circuits. (sample code is to be given).
9. Example of Abstraction: Laptop: Outer look of laptop, screen size, keyboard.

Q: Why Encapsulation is called Data hiding in Java?
Ans:

Encapsulation is a technique whereby the implementation details of a class are kept hidden from the user. In other words, the variable of the class is hidden and is accessed only by using methods. Therefore, it is also known as data hiding.

Q: What are the advantages of using Encapsulation?
Ans:

Encapsulation binds or wraps the data and actions in a single unit using variables and methods which makes the use of data simpler and more flexible. Using encapsulation makes it easier to make the changes without affecting different classes. Maintaining data becomes easier as many different packages are created. All the variables must be private, and they should be handled by the only method in the class.

Q: How to achieve Encapsulation in Java with Example?
Ans:

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 the variables. Let's see the code for better understanding:

public class Student {
    private String name;
    public String getName() {
        return name;
    }
    public void
    setName(String name) {
        this.name = name;
    }
}
class Test {
    public static void main(String[] args) {
        Student s = new
        Student();
        s.setName("Anjua desia");
        System.out.println(s.getName());
    }
}

As per the above code, one can see that, a class Student has a private variable name. Next is getter and setter to get and set the name of a student. With the help of these examples getter and setter methods are used to access name variables..

Q: What is a tightly encapsulated class?
Ans:

The tightly encapsulated class is where all the data members (variables) are declared as private. Whether getter and setters are modified or not.

Q: How does getter and setter functions help in encapsulation?
Ans:

In encapsulation, the getters and setters method is because to hide the attributes of an object class from other classes so that no accidental modification of the data happens by methods in other classes. Example:

1. Declare class variables/attributes as private.
2. Provide public get and set methods to access and update the value of a private variable.

public class Person {
  private String name; // private = restricted access

  // Getter
  public String getName() {
    return name;
  }

  // Setter
  public void setName(String newName) {
    this.name = newName;
  }
}

Q: Is Encapsulation violating reflection?
Ans:

Encapsulation wants to give modules a safe space and Reflection wants to break into all code. Thus the manipulation of the data is done at one place unknowing to other members of variables. Encapsulation principles are broken using the reflection as it can access the private classes without setting getter and setter methods.

Q: Which design pattern is based on encapsulation in Java?
Ans:

Design pattern in encapsulation is a reusable solution for rectifying the problem occurring within the context. The design pattern is mainly used for creating layers of classes and modifying the changes becomes easier as a specific class is corrected/modified without affecting other classes.

Q: What is the difference between Encapsulation and Polymorphism?
Ans:

Packaging data and methods in a single unit are Encapsulation. Their own methods are used for accessing the data which are hidden in the objects.

The word polymorphism means Poly means many and morph means form.

Polymorphism means the ability to take more than one form by using a single interface. when single or many types are not defined by name it represents any type by using abstract symbols. Polymorphism is a process used for implementing inherited data.