Private access modifier in Java - Mini Project: Build & Apply

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Understanding the Private Access Modifier in Java

📖 Scenario: Imagine you are creating a simple Java class to represent a bank account. You want to keep the account balance safe so that it cannot be changed directly from outside the class.

🎯 Goal: You will create a Java class with a private variable to store the balance, then add methods to safely access and update the balance.

📋 What You'll Learn

Create a class called BankAccount

Add a private variable called balance of type double

Add a public method getBalance() to return the current balance

Add a public method deposit(double amount) to add money to the balance

Add a public method withdraw(double amount) to subtract money from the balance if enough funds exist

Print the balance after deposits and withdrawals

💡 Why This Matters

🌍 Real World

In real banking software, sensitive data like account balances must be protected from direct changes to avoid errors or fraud.

💼 Career

Understanding access modifiers like private is essential for writing secure and maintainable code in professional Java development.

1

Create the BankAccount class with a private balance variable

Create a class called BankAccount with 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 variable balance to restrict access.

2

Add a public method to get the balance

Add a public method called getBalance() that returns the value of the private variable balance.

Java

public class BankAccount {
    private double balance = 0.0;

    // Your code here
}

💡 Need a hint?

The method should be public so other classes can call it.

3

Add deposit and withdraw methods

Add two public methods: deposit(double amount) to add amount to balance, and withdraw(double amount) to subtract amount from balance only if balance is enough.

Java

public class BankAccount {
    private double balance = 0.0;

    public double getBalance() {
        return balance;
    }

    // Your code here
}

💡 Need a hint?

Use an if statement in withdraw to check if there is enough balance.

4

Create a main method to test the BankAccount class

Add a main method inside BankAccount that creates an object called account, deposits 100.0, withdraws 30.0, and then prints the balance using System.out.println.

Java

public class BankAccount {
    private double balance = 0.0;

    public double getBalance() {
        return balance;
    }

    public void deposit(double amount) {
        balance += amount;
    }

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

    // Your code here
}

💡 Need a hint?

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