Custom getters and setters in Kotlin - Mini Project: Build & Apply

Custom getters and setters

📖 Scenario: You are creating a simple Kotlin class to represent a bank account. You want to control how the balance is accessed and changed by using custom getters and setters.

🎯 Goal: Build a Kotlin class BankAccount with a balance property. Use custom getter to show the balance with a message, and a custom setter to prevent setting a negative balance.

📋 What You'll Learn

Create a class called BankAccount with a balance property of type Double initialized to 0.0

Add a custom getter for balance that returns the balance as a string with the message: "Current balance: $X" where X is the balance

Add a custom setter for balance that only updates the balance if the new value is not negative

Create an instance of BankAccount, set the balance to 100.0, then try to set it to -50.0, and finally print the balance

💡 Why This Matters

🌍 Real World

Bank accounts and financial apps often need to control how money values are accessed and changed to avoid errors or fraud.

💼 Career

Understanding custom getters and setters is important for writing safe and clear Kotlin code in real-world applications.

1

Create the BankAccount class with a private balance

Create a Kotlin class called BankAccount with a balance property of type Double initialized to 0.0.

Kotlin

class BankAccount {
    // Your code here
}

Need a hint?

Use var balance: Double = 0.0 inside the class.

2

Add a custom getter for balance

Add a custom getter for the balance property that returns a String with the message: "Current balance: $X" where X is the current balance value.

Kotlin

class BankAccount {
    var balance: Double = 0.0

    // Your code here
}

Need a hint?

Create a new val displayBalance with a custom getter that returns the message string.

3

Add a custom setter to prevent negative balance

Add a custom setter for the balance property that only updates the balance if the new value is not negative. If the new value is negative, do not change the balance.

Kotlin

class BankAccount {
    var balance: Double = 0.0
        set(value) {
            // Your code here
        }

    val displayBalance: String
        get() = "Current balance: \$${balance}"
}

Need a hint?

Use set(value) { if (value >= 0) field = value } to protect the balance.

4

Create an instance, set balances, and print

Create an instance of BankAccount called account. Set the balance to 100.0, then try to set it to -50.0. Finally, print account.displayBalance.

Kotlin

class BankAccount {
    var balance: Double = 0.0
        set(value) {
            if (value >= 0) {
                field = value
            }
        }

    val displayBalance: String
        get() = "Current balance: \$${balance}"
}

// Your code here

Need a hint?

Remember to create account, set balance twice, and print account.displayBalance.