Encapsulation in Java

Encapsulation is one of the four fundamental Object-Oriented Programming (OOP) principles and plays a crucial role in designing robust and maintainable Java code. Encapsulation in java is a mechanism of binding all data (fields) and the methods to manipulating data together into a single Class. Encapsulation is one of the four fundamental object oriented programming concepts.

The data of a class will be hidden from external classes, it is not directly accessible by external code. It can only be accessed through public methods of their class.

Encapsulation provides the security by hiding the internal data and implementation details from external code to avoid inadvertent changes. By calling public methods of a class, any external entity can access the data but cannot modify it.

Key Characteristics of Encapsulation
  • Data Hiding : Encapsulation hides the internal state of an object, allowing controlled access only through well-defined methods

  • Access Modifiers : Access modifiers (such as private, protected, and public) are used to control the visibility of classes, methods, and fields.

  • Getters and Setters : Getter methods allow access to the values of private fields, and setter methods allow modification of these values. This allows controlled and validated access to the internal state
Advantages of Encapsulation
  • Modularity and Maintainability : Encapsulation promotes modularity by organizing code into self-contained units (classes). Each class represents a module with a well-defined interface. This makes it easier to understand, modify, and maintain the code.

  • Control over Access : By using access modifiers, encapsulation provides control over the visibility of the internal components of a class. This prevents unauthorized access and modification of data, ensuring that the object's state remains consistent.

  • Data Validation : Encapsulation allows the implementation of getter and setter methods, enabling data validation. This ensures that only valid and acceptable values are set for the object's attributes.

  • Flexibility in Implementation : Encapsulation allows the internal implementation details of a class to change without affecting the external code that uses the class. This flexibility is crucial for evolving and maintaining large codebases.

How to achieve encapsulation in Java

  • Declare the member variables of class as private.

  • Expose some public methods for external world to interact with your class.

  • Keep you implementation details hidden inside private methods.

Java program for encapsulation

class Rectangle {
  // private data
  private int length, width;

  public void setLength(int length) {
    this.length = length;

  public void setWidth(int width) {
    this.width = width;
  public int calculateArea() {
    return length * width;
public class EncapsulationJava {
  public static void main(String[] args) {
    Rectangle rect = new Rectangle();
    // Invoke public methods
    System.out.println("Area = " + rect.calculateArea());
Area = 200

In the above program, we have created a class called Rectangle, which provides a public method to calculate area of rectangle. Member variable length and width are declared with private modifier. Hence, they cannot be accessed from outside.

The public method setLength() and setWidth() are the only access points of the instance variables of the Rectangle class. Any class that wants to access the variables should access them through these getters methods. Making length and width fields private allowed us to restrict unauthorized access from outside the class.

Encapsulation and Immutable Classes

  • Immutable Classes : An immutable class is a class whose instances cannot be modified after creation. Immutable classes often use encapsulation to achieve immutability. All fields are made private, and modifications are prevented by not providing setter methods.

  • Example of an Immutable Class : Let's create an example of an immutable class ImmutablePoint representing a 2D point. Once a point is created, its coordinates cannot be changed.
    public final class ImmutablePoint {
        private final int x;
        private final int y;
        public ImmutablePoint(int x, int y) {
            this.x = x;
            this.y = y;
        public int getX() {
            return x;
        public int getY() {
            return y;
    In this example, the ImmutablePoint class has private final fields (x and y), and there are no setter methods. The values are set only through the constructor, making instances of this class immutable.

  • Benefits of Immutable Classes
    • Immutable classes are inherently thread-safe as their state cannot be modified.

    • Once created, the state of an immutable object remains constant, leading to predictable and reliable behavior.

    • Immutability simplifies the design of classes by eliminating the need for complex state-changing operations.

Best Practices for Encapsulation

  • Minimize Accessibility : Make attributes private whenever possible and provide controlled access through getter and setter methods. Minimizing accessibility helps in controlling modifications and enforcing encapsulation.

  • Use Validation in Setters : When providing setter methods, include validation logic to ensure that only valid values are accepted. This prevents the object from being in an inconsistent or invalid state.

  • Think About Immutability : Consider making classes immutable when it makes sense. Immutable classes are often simpler to reason about and can lead to more robust and predictable code.

  • Favor Composition over Inheritance : Encapsulation encourages the use of composition over inheritance. Rather than exposing the internal details of a class, encapsulate them and provide well-defined interfaces for composition.

  • Document Your Classes : Document the intended use of your classes, including the purpose of attributes and any constraints on their values. Clear documentation helps other developers understand how to use your classes correctly.


Encapsulation is a fundamental principle in Java and object-oriented programming, providing a mechanism for bundling data and methods into cohesive units. By properly encapsulating classes, you create modular, maintainable, and flexible code that can adapt to changing requirements. The use of access modifiers, getters, and setters allows you to control access to the internal state of objects, promoting a clean and controlled interface.

Understanding and applying encapsulation is an essential skill for Java developers, and it forms the foundation for building scalable and reliable software systems. Whether you're working on small projects or large-scale applications, mastering encapsulation contributes to the creation of robust and maintainable code.