Encapsulation and Access Modifiers

Site Admin · 11 Sep 2026 · 11 views

Why Hide Data?

Encapsulation bundles the data of a class with the methods that operate on it, and keeps the data private. Outsiders cannot assign invalid values accidentally because they must go through controlled methods called getters and setters.

Without Encapsulation (the problem)

class BankAccount {
    public double balance; // anyone can break the rules
}
BankAccount a = new BankAccount();
a.balance = -500;          // negative balance, nothing stops it!

With Encapsulation (the fix)

class BankAccount {
    private double balance; // hidden from outside

    public double getBalance() { return balance; }

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

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

Now negative deposits are simply ignored, and callers can never put the account into an invalid state directly.

The Access Modifiers

Modifier	Same class	Same package	Subclass	Anywhere
private	Yes	No	No	No
(default)	Yes	Yes	No	No
protected	Yes	Yes	Yes	No
public	Yes	Yes	Yes	Yes

Getters and Setters

class Person {
    private int age;

    public int getAge() { return age; }

    public void setAge(int age) {
        if (age >= 0 && age <= 120) {
            this.age = age;
        }
    }
}