Custom Exception Hierarchies

Custom exception hierarchies

Model domain failures as types, not strings:

public class OrderException extends RuntimeException {
    public OrderException(String message) { super(message); }
    public OrderException(String message, Throwable cause) { super(message, cause); }
}

public final class InsufficientFundsException extends OrderException {
    private final int shortfallCents;
    public InsufficientFundsException(String message, int shortfallCents) {
        super(message);
        this.shortfallCents = shortfallCents;
    }
    public int shortfallCents() { return shortfallCents; }
}

Callers can now catch at the right granularity: catch (InsufficientFundsException e) to show a friendly message, or catch (OrderException e) for all order failures.

Keep hierarchy shallow (base + 2–3 leaf types), extend RuntimeException unless the caller can genuinely recover, and carry data on the exception (like shortfallCents) instead of forcing callers to parse the message.