← Back to Overview

Java Program - Encapsulation (Private Members)

Concept Explanation

What is it?

Encapsulation is one of the four fundamental OOP concepts. It involves bundling the data (variables) and the methods that act on the data into a single unit (class) and restricting direct access to some of an object's components.

Why is it important?

It protects data from accidental corruption. By making fields private and providing public methods to access them, you can control how fields are accessed or modified (e.g., preventing a negative age).

---

Implementations

Java (JDK 17)

class Student {
    // Private variables (Data Hiding)
    private int id;
    private String name;

    // Public Getter for ID
    public int getId() {
        return id;
    }

    // Public Setter for ID with Validation
    public void setId(int id) {
        if (id > 0) {
            this.id = id;
        } else {
            System.out.println("Error: Invalid ID. Must be positive.");
        }
    }

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

    // Public Setter for Name
    public void setName(String name) {
        this.name = name;
    }
}

public class EncapsulationDemo {
    public static void main(String[] args) {
        Student s1 = new Student();

        // s1.id = 101; // Compile Error: id has private access

        s1.setId(101);
        s1.setName("Alice");

        System.out.println("Student ID: " + s1.getId());
        System.out.println("Student Name: " + s1.getName());

        // Test Validation
        s1.setId(-5); // Will print error message
    }
}

---

Explanation

• Private Fields: id and name cannot be accessed directly by other classes.
• Public Methods: getId() and setId() provide a controlled interface.
• Logic in Setters: The setId method checks if the input is valid before assignment. This logic would be impossible with direct public field access.

---

Related Concepts

• Using Constructors
• Using Methods

---

"Encapsulation is the first step towards a robust and secure design." - Anonymous