Creating custom exception class in Java - Try It Yourself

Creating custom exception class

📖 Scenario: Imagine you are building a simple banking application. You want to handle errors when someone tries to withdraw more money than their account balance.

🎯 Goal: You will create a custom exception class called InsufficientFundsException and use it to show a clear error message when a withdrawal is not possible.

📋 What You'll Learn

Create a custom exception class named InsufficientFundsException that extends Exception.

Add a constructor to InsufficientFundsException that accepts a String message and passes it to the superclass.

Create a class called BankAccount with a private double variable balance.

Add a constructor to BankAccount that sets the initial balance.

Add a method withdraw in BankAccount that throws InsufficientFundsException if withdrawal amount is greater than balance.

Add a method getBalance to return the current balance.

Write code to test withdrawing money and catching the custom exception.

💡 Why This Matters

🌍 Real World

Custom exceptions help make error messages clearer and more specific in real applications like banking, shopping carts, or user input validation.

💼 Career

Understanding how to create and use custom exceptions is important for writing robust Java programs and is a common skill required in software development jobs.

1

Create the custom exception class

Create a public class called InsufficientFundsException that extends Exception. Add a constructor that takes a String message and passes it to super(message).

Java

// Your code here

Need a hint?

Remember to extend Exception and call super(message) inside the constructor.

2

Create the BankAccount class with balance

Create a public class called BankAccount. Add a private double variable named balance. Add a constructor that takes a double initialBalance and sets balance to it.

Java

public class InsufficientFundsException extends Exception {
    public InsufficientFundsException(String message) {
        super(message);
    }
}

// Your code here

Need a hint?

Use private double balance; and set it in the constructor.

3

Add withdraw method with exception

In the BankAccount class, add a public method withdraw that takes a double amount and throws InsufficientFundsException. If amount is greater than balance, throw new InsufficientFundsException with message "Not enough balance". Otherwise, subtract amount from balance. Also add a public method getBalance that returns the current balance.

Java

public class InsufficientFundsException extends Exception {
    public InsufficientFundsException(String message) {
        super(message);
    }
}

public class BankAccount {
    private double balance;

    public BankAccount(double initialBalance) {
        this.balance = initialBalance;
    }

    // Add withdraw and getBalance methods below
    // Your code here
}

Need a hint?

Check if amount is more than balance. If yes, throw the exception. Otherwise, reduce the balance.

4

Test withdrawing and catching exception

Create a public class Main with a main method. Inside main, create a BankAccount object with initial balance 1000. Try to withdraw 1500 inside a try block. Catch InsufficientFundsException and print its message. Also print the remaining balance after the withdrawal attempt.

Java

public class InsufficientFundsException extends Exception {
    public InsufficientFundsException(String message) {
        super(message);
    }
}

public class BankAccount {
    private double balance;

    public BankAccount(double initialBalance) {
        this.balance = initialBalance;
    }

    public void withdraw(double amount) throws InsufficientFundsException {
        if (amount > balance) {
            throw new InsufficientFundsException("Not enough balance");
        }
        balance -= amount;
    }

    public double getBalance() {
        return balance;
    }
}

public class Main {
    public static void main(String[] args) {
        // Your code here
    }
}

Need a hint?

Use a try block to call withdraw and catch InsufficientFundsException. Print the exception message and then print the balance.