What makes a useful first OOP project?
The key idea
A useful project gives an object rules worth protecting. For this exercise, model one fictional library copy that can be available or on loan. The goal is to understand valid state changes, not to build an entire library management product.
Work with invented identifiers. There is no need to collect real borrower information, implement payments or connect to a database for this learning task.
Define the state before the methods
The copy has an identifier and a current loan state. A borrowing operation succeeds only when the copy is available. A return succeeds only when it is on loan. Failed operations leave the state unchanged.
| Current state | Requested action | Result | New state |
|---|---|---|---|
| Available | Borrow | Success | On loan |
| On loan | Borrow | Refused | On loan |
| On loan | Return | Success | Available |
| Available | Return | Refused | Available |
This table is the centre of the specification. If your code disagrees with it, decide whether the code or the specification needs correction.
Choose a small interface
Possible methods are borrow, returnCopy and isAvailable. The exact names matter less than their documented behaviour. Return a result that the caller can inspect rather than silently pretending every request succeeded.
Keep the state private and avoid a public setter that allows any arbitrary combination. For a first exercise, an enumeration can express the two states clearly. Add borrower information only when you have specified how it affects the rules.
Write acceptance cases before implementation
- A new copy begins available.
- Borrowing it once succeeds.
- Borrowing again fails without changing the state.
- Returning it succeeds.
- Returning again fails without changing the state.
Also check that operations on one copy do not change another. This tests the distinction between per-object state and accidentally shared data.
Add one extension carefully
Suppose you add reservations. Decide whether an available reserved copy can be borrowed by anyone or only by the reservation holder. You now need more states or a richer rule, plus additional test cases.
Do not insert a reservation flag and assume the combinations make sense. Write the transitions first. An extension should make the model more accurate, not merely increase the number of fields.
Keep the exercise's limits clear
This single-process model does not solve concurrent borrowing, persistence or recovery after a crash. Those are separate engineering problems. A beginner can complete the object model without claiming to have a production library system.
Gammal Tech's OOP course follows C++. Use this exercise to demonstrate encapsulation and valid transitions. When you can explain why a second borrow fails and why another object is unaffected, you have evidence of understanding beyond a class definition copied from a lesson.
References and course details
Use these references for further study. The examples and exercises in this article are educational; consult the catalogue for course details.