Build a BankAccount class

Description: Create a class BankAccount with a private balance. Add deposit(amount) and withdraw(amount). Refuse a negative deposit and a withdraw bigger than the balance (throw an exception). Test it.

Hint:

• Keep the field private and give a getter only.
• Throw IllegalArgumentException and IllegalStateException.

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Solution

class BankAccount {
    private double balance;

    void deposit(double amount) {
        if (amount <= 0) throw new IllegalArgumentException("Deposit must be positive");
        balance += amount;
    }

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

    double getBalance() { return balance; }
}

public class Main {
    public static void main(String[] args) {
        BankAccount acc = new BankAccount();
        acc.deposit(1000);
        acc.withdraw(250);
        System.out.println(acc.getBalance());

        try {
            acc.withdraw(5000);
        } catch (IllegalStateException e) {
            System.out.println("Error: " + e.getMessage());
        }
        try {
            acc.deposit(-5);
        } catch (IllegalArgumentException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

How it works

• The balance is private, so the only way to change it is through the two methods which check the values.

Read Java Encapsulation.

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