Why custom exceptions are needed in Java - See It in Action

Why Custom Exceptions Are Needed

📖 Scenario: Imagine you are building a simple banking application. You want to handle errors like when someone tries to withdraw more money than they have. Java has built-in exceptions, but sometimes you need your own special error messages to make your program clearer and easier to fix.

🎯 Goal: You will create a custom exception called InsufficientFundsException to show how custom exceptions help make your program clearer and handle specific problems better.

📋 What You'll Learn

Create a custom exception class called InsufficientFundsException that extends Exception

Create a class called BankAccount with a balance variable

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

Write code to catch the InsufficientFundsException and print a clear message

💡 Why This Matters

🌍 Real World

Custom exceptions are used in real banking software to handle errors like insufficient funds clearly and safely.

💼 Career

Understanding custom exceptions is important for writing clean, maintainable Java code and is a common skill required in software development jobs.

1

Create the InsufficientFundsException class

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

Java

// Your code here

Need a hint?

Remember, to create a custom exception, extend the Exception class and call super(message) in the constructor.

2

Create the BankAccount class with a balance

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

Java

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

// Your code here

Need a hint?

Define the balance variable and set it in the constructor using this.balance = initialBalance.

3

Add the withdraw method that throws InsufficientFundsException

In the BankAccount class, add a public method called withdraw that takes a double parameter amount and throws InsufficientFundsException. Inside the method, check if amount is greater than balance. If yes, throw a new InsufficientFundsException with the message "Not enough balance". Otherwise, subtract amount from 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 the withdraw method below
    // Your code here
}

Need a hint?

Use throws InsufficientFundsException in the method signature and throw the exception when amount is too big.

4

Test the withdraw method and catch the exception

Create a public class called Main with a main method. Inside main, create a BankAccount object with a balance of 100. Use a try-catch block to call withdraw(150) on the account. Catch InsufficientFundsException and print the exception message.

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;
    }
}

// Your code here

Need a hint?

Use a try-catch block to call withdraw and catch InsufficientFundsException. Print the exception message with e.getMessage().