How do you create and throw a custom exception in Java? Java में custom exception कैसे बनाएं और throw करें?

Custom exceptions are created by extending Exception (for checked) or RuntimeException (for unchecked), letting you represent domain-specific error conditions clearly.

// Custom CHECKED exception - must be declared or caught
class InsufficientFundsException extends Exception {
    public InsufficientFundsException(String message) {
        super(message);
    }
}

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

    public void withdraw(double amount) throws InsufficientFundsException {
        if (amount > balance) {
            throw new InsufficientFundsException(
                'Cannot withdraw ' + amount + ', balance is only ' + balance);
        }
        balance -= amount;
    }
}

public class Main {
    public static void main(String[] args) {
        BankAccount account = new BankAccount(100);
        try {
            account.withdraw(150);
        } catch (InsufficientFundsException e) {
            System.out.println(e.getMessage());
        }
    }
}

// Custom UNCHECKED exception - no 'throws' declaration required
class InvalidAgeException extends RuntimeException {
    public InvalidAgeException(String message) {
        super(message);
    }
}

public void setAge(int age) {
    if (age < 0) {
        throw new InvalidAgeException('Age cannot be negative: ' + age);
    }
}

// Adding custom fields to an exception
class InsufficientFundsException2 extends Exception {
    private final double shortfall;
    public InsufficientFundsException2(double shortfall) {
        super('Short by ' + shortfall);
        this.shortfall = shortfall;
    }
    public double getShortfall() { return shortfall; }
}