What is Encapsulation?

Encapsulation is the process of wrapping data (fields) and code (methods) together in a single unit (a class), while restricting access to internal object details.

In Java, this is typically done by:

• Declaring fields private.

• Providing public getters and setters to access and modify those fields.

This helps protect the object’s internal state from external misuse.

Why Use Encapsulation?

• Improves security – You control how data is modified.

• Increases maintainability – You can change internal implementation without affecting outside code.

• Simplifies debugging – Changes to a variable go through one controlled point.

Access Modifiers in Java

private: Within the same class only

default: Package-private (within the same package)

protected: Same package or subclasses

public: From anywhere

public class BankAccount {
    public double balance; // Exposed directly

    public void deposit(double amount) {
        balance += amount;
    }
}
// Anyone can do:
BankAccount b = new BankAccount();
b.balance = -5000; // Not safe!

Example: With Encapsulation (GOOD)

public class BankAccount {
    private double balance;

    public void deposit(double amount) {
        if (amount > 0) balance += amount;
    }

    public void withdraw(double amount) {
        if (amount > 0 && amount <= balance) balance -= amount;
    }

    public double getBalance() {
        return balance;
    }
}

Summary

• Encapsulation = hiding data + exposing safe interfaces (getters/setters).

• Use private for fields and control access through public methods.

• This protects object integrity and aligns with good design principles

Assignment: Lesson 3 – Encapsulation

Objective:

Practice encapsulating data in a class using private fields and public methods.

Part 1: Conceptual Questions

Write answers in a comment or separate file:

1. What is encapsulation and why is it important?

2. What keyword is used to make a field hidden from outside access?

3. Why shouldn’t we expose fields like public int age; directly?

Part 2: Coding Task

Create a Person class with:

• Private fields: name (String), age (int)

• Public methods:

  • setName(String name) – sets the name

  • setAge(int age) – sets age if age ≥ 0

  • getName() – returns the name

  • getAge() – returns the age

In your main() method:

• Create a Person object

• Set name and age using the setter methods

• Print the name and age using getters

Github: https://github.com/tuanbeovnn/java-bootcamp/tree/java-bootcamp-oop-chapter3