Encapsulation

Think about a Tylenol or Advil capsule. Inside the plastic shell is the actual medicine (the data). You don't interact with the powder directly; you just take the capsule. The shell protects the contents from the outside world and ensures you use the medicine exactly how it was intended.

In Java, Encapsulation means:

1. Hiding the data (variables) by making them private.

2. Providing access to that data only through "doors" called Getters and Setters.

Why do this?

If I have a BankEmployee class with a balance variable, I don't want anyone to just type account.balance = 1000000;. By making it private, I force them to use a method where I can check their identity or verify that the amount is valid before changing it.

The Access Modifiers

• public: Accessible from anywhere in your project.

• private: Accessible only inside that specific class. No one else can see it.

The Code Example:

class BankAccount {
    // 1. Private variables (Hidden from the outside)
    private String accountHolder;
    private double balance;

    // 2. Constructor
    public BankAccount(String name, double startingBalance) {
        this.accountHolder = name;
        this.balance = startingBalance;
    }

    // 3. Getter Method (The "Viewing Window")
    public double getBalance() {
        return balance;
    }

    // 4. Setter Method (The "Controlled Door")
    public void deposit(double amount) {
        if (amount > 0) {
            balance += amount;
            System.out.println("Successfully deposited $" + amount);
        } else {
            System.out.println("Invalid amount! You can't deposit negative money.");
        }
    }
}

public class Main {
    public static void main(String[] args) {
        BankAccount myAccount = new BankAccount("John Doe", 500.00);

        // This would cause a COMPILE ERROR:
        // myAccount.balance = 5000; 

        // We must use the public methods
        myAccount.deposit(150.00);
        myAccount.deposit(-50.00); // This will trigger the safety check

        System.out.println("Final Balance: $" + myAccount.getBalance());
    }
}

Expected Output:

Successfully deposited $150.0
Invalid amount! You can't deposit negative money.
Final Balance: $650.0