Encapsulation

Data hiding and access control

Encapsulation

Encapsulation bundles data (attributes) and methods that operate on that data into a single unit (class), while restricting direct access to some components. It protects internal state from unauthorized access and modification.

java

// Encapsulation with Getters/Setters
public class BankAccount {
    // Private fields — hidden from outside
    private String accountNumber;
    private double balance;
    private String owner;

    public BankAccount(String accountNumber, String owner, double initialBalance) {
        this.accountNumber = accountNumber;
        this.owner = owner;
        this.balance = initialBalance;
    }

    // Public getter — controlled read access
    public double getBalance() {
        return balance;
    }

    // Public method — controlled write with validation
    public void deposit(double amount) {
        if (amount <= 0) {
            throw new IllegalArgumentException("Deposit must be positive");
        }
        balance += amount;
    }

    public boolean withdraw(double amount) {
        if (amount <= 0 || amount > balance) {
            return false; // Insufficient funds or invalid amount
        }
        balance -= amount;
        return true;
    }

    // No setter for accountNumber — immutable after creation
    public String getAccountNumber() {
        return accountNumber;
    }
}

private: Accessible only within the same class
protected: Accessible within the same class, subclasses, and same package
public: Accessible from anywhere
default (package-private): Accessible within the same package only

💡

Always make fields private and provide public getters/setters only when necessary. This allows you to add validation, logging, or change the internal representation without breaking external code.