What is the primary reason to use defensive copying when returning a list from a class?

• To save memory

• To prevent external modification of the internal state

• To confuse other developers

• To automatically sort the list

If you return a list directly from a class and another part of your code modifies it, what OOP principle is being violated?

• Encapsulation

• Polymorphism

• Abstraction

• Inheritance

Which collection is better if you’re doing frequent insertions and deletions in the middle of the list?

• ArrayList

• LinkedList

• HashMap

• Vector

A class allows you to borrow books. You now want to borrow multiple books at once. What should you add?

• A loop in the main method

• A new method like borrowMultipleBooks()

• Delete all books

• Make the list static

What helps prevent an object from reaching an invalid state?

• Logging everything

• Skipping validations

• Enforcing business rules

• Using only primitive data types

Why use getters/setters instead of public variables?

• They're shorter to write

• They confuse the user

• They allow control over how variables are accessed/modified

• They are required by Java

What does it mean for an object to be immutable?

• It can’t be accessed by other classes

• It can’t be changed after it's created

• It’s slower to execute

• It throws exceptions when used

—Defensive copying—

public List<String> getAuthors() {

// ?

}

Which line correctly implements defensive copying?

• return authors;

• return authors.clone();

• return new ArrayList<>(authors);

• return null;

public class Library {

private List<String> books;

// ?

}

Which constructor properly initializes books?

• public Library() { books.clear(); }

• public Library() { books = new ArrayList<>(); }

• Library() => books = [];

• new Library() { books = null; }

public void setTitle(String title) {

// ?

}

Which code correctly throws an exception for invalid input?

• this.title = title;

• if (title.length() == 0) return;

• if (title == null) throw new IllegalArgumentException("Invalid title");

• System.out.println("Invalid title");