The correct answer is to define an abstract method `getBorrowMessage()` in `LibraryItem` and implement it in `Book` and `DVD`, then call that method in `borrow()`. This design correctly applies the Open/Closed Principle in Java by leveraging inheritance and polymorphism: the parent class declares an abstract contract, and each subclass provides its own behavior through method overriding, allowing the `borrow()` method to work with any future `LibraryItem` subtype without modification. On the Oracle Java Foundations 1Z0-811 exam, this question tests your understanding of how abstract methods enable polymorphic dispatch—a core concept that distinguishes proper object-oriented design from brittle `instanceof` checks. A common trap is thinking you need conditional logic in the borrower, but the exam rewards the polymorphic approach because it keeps code closed for modification but open for extension. Memory tip: "Abstract the action, inherit the reaction"—let the subclass decide what message to return.
1Z0-811 Object-Oriented Programming Practice Question
This 1Z0-811 practice question tests your understanding of object-oriented programming. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A development team is building a library management system. The system has classes 'LibraryItem', 'Book', and 'DVD'. LibraryItem has a method 'getTitle()' that returns the title. Book and DVD extend LibraryItem. The team wants to ensure that when a LibraryItem is borrowed, a message specific to its type is displayed. They have a 'Borrower' class with a method 'borrow(LibraryItem item)', which currently calls 'item.getTitle()' and prints the title. Now they need to display 'Book borrowed' or 'DVD borrowed' based on the actual item type. They want to avoid using 'instanceof' checks in the 'borrow' method to keep it open for new item types. Which design should they use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Define an abstract method 'getBorrowMessage()' in LibraryItem, and implement it in Book and DVD. Call that method in borrow().
Option C is correct because it applies the Open/Closed Principle: LibraryItem defines an abstract getBorrowMessage() method, and each subclass provides its own implementation. The borrow() method calls this polymorphic method without needing instanceof or type checks, so adding new item types (e.g., Magazine) only requires implementing getBorrowMessage() in the new subclass without modifying existing code.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Add a String field 'type' to LibraryItem and set it in each subclass constructor. In borrow(), check the field.
Why it's wrong here
Still requires conditional logic, not extensible for new types without modifying borrow().
✗
Use a switch statement on the class name in borrow().
Why it's wrong here
Requires modification when new types added; not open for extension.
✓
Define an abstract method 'getBorrowMessage()' in LibraryItem, and implement it in Book and DVD. Call that method in borrow().
Why this is correct
Polymorphism allows new subclasses to define their own message without changing borrow().
Related concept
Read the scenario before looking for a memorised answer.
✗
Override the 'borrow' method in each subclass and call a different method.
Why it's wrong here
Overriding borrow in subclasses would duplicate borrowing logic; not clean.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Oracle often tests the Open/Closed Principle by presenting options that appear to work (like a type field or switch on class name) but violate extensibility, tempting candidates to choose a quick fix instead of the polymorphic solution.
Detailed technical explanation
How to think about this question
Polymorphism via abstract methods leverages dynamic dispatch: at runtime, the JVM uses the vtable (virtual method table) of the actual object to invoke the correct overridden method. This design is fundamental to the Strategy pattern and frameworks like Java Collections (e.g., List.forEach() calling the overridden behavior of ArrayList or LinkedList). In real-world library systems, adding a new item type (e.g., Magazine) requires only implementing getBorrowMessage() in the new subclass, with zero changes to the Borrower class.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 1Z0-811 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Object-Oriented Programming — This question tests Object-Oriented Programming — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Define an abstract method 'getBorrowMessage()' in LibraryItem, and implement it in Book and DVD. Call that method in borrow(). — Option C is correct because it applies the Open/Closed Principle: LibraryItem defines an abstract getBorrowMessage() method, and each subclass provides its own implementation. The borrow() method calls this polymorphic method without needing instanceof or type checks, so adding new item types (e.g., Magazine) only requires implementing getBorrowMessage() in the new subclass without modifying existing code.
What should I do if I get this 1Z0-811 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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