Encapsulation best practices in Java - Mini Project: Build & Apply

Encapsulation Best Practices in Java

📖 Scenario: You are creating a simple Java class to represent a bank account. You want to protect the account's balance so that it cannot be changed directly from outside the class. This is a common real-world need to keep data safe and controlled.

🎯 Goal: Build a Java class called BankAccount that uses encapsulation best practices: private fields, public getter and setter methods, and validation inside the setter.

📋 What You'll Learn

Create a class called BankAccount with a private double field named balance

Add a public method getBalance() that returns the current balance

Add a public method setBalance(double amount) that sets the balance only if the amount is zero or positive

Do not allow direct access to the balance field from outside the class

💡 Why This Matters

🌍 Real World

Encapsulation is used in real-world software to protect sensitive data like bank balances, passwords, or personal information.

💼 Career

Understanding encapsulation is essential for writing safe, maintainable, and professional Java code in software development jobs.

1

Create the BankAccount class with a private balance field

Create a public class called BankAccount and inside it declare a private double variable named balance initialized to 0.0.

Java

public class BankAccount {
    // Your code here
}

Need a hint?

Use the keyword private before the double balance variable to hide it from outside the class.

2

Add a public getter method for balance

Inside the BankAccount class, add a public method called getBalance() that returns the value of the balance variable.

Java

public class BankAccount {
    private double balance = 0.0;

    // Your code here
}

Need a hint?

The getter method should be public and return the private balance value.

3

Add a public setter method with validation

Inside the BankAccount class, add a public method called setBalance(double amount) that sets the balance only if amount is greater than or equal to 0. Otherwise, do not change the balance.

Java

public class BankAccount {
    private double balance = 0.0;

    public double getBalance() {
        return balance;
    }

    // Your code here
}

Need a hint?

Use an if statement to check if amount is not negative before setting balance.

4

Test the BankAccount class by setting and getting balance

Create a main method inside the BankAccount class. Inside it, create a BankAccount object called account. Use setBalance(100.0) to set the balance, then print the balance using getBalance().

Java

public class BankAccount {
    private double balance = 0.0;

    public double getBalance() {
        return balance;
    }

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

    // Your code here
}

Need a hint?

Use System.out.println(account.getBalance()); to print the balance.