Encapsulation: private fields, getters, setters

1 Learn

Encapsulation means keeping an object's data safe inside it. Fields are made private so outside code cannot change them directly.

Public getter methods read the data; setter methods change it — and can check the value first.

Want more detail? Open the full lesson

2 See the Code

Java

class Account {
    private double balance;

    public double getBalance() {
        return balance;
    }

    public void deposit(double amount) {
        if (amount > 0) {
            balance += amount;
        } else {
            System.out.println("Invalid amount");
        }
    }
}

public class Bank {
    public static void main(String[] args) {
        Account acc = new Account();
        acc.deposit(500);
        acc.deposit(-50);
        System.out.println(acc.getBalance());
    }
}

balance is private — acc.balance = 1000000 would not compile outside the class.
deposit() rejects negative amounts, protecting the data.

Output

Invalid amount
500.0

3 Practice

Make a Student class with private marks, getMarks() and setMarks() that only accepts 0 to 100.

Try it in your own Java setup or write it in the Practice Notebook.

4 Quick Check

1. Encapsulation mainly protects...
2. Which access modifier hides a field from other classes?

Step 5

Answer and check the Quick Check above to unlock this.

Day 17