Complete Class with an ArrayList Field

An ArrayList instance variable lets a class grow and shrink its collection at runtime. The constructor initializes it (usually empty); methods add to it, remove from it, search it, or compute over it.

The class is responsible for protecting the ArrayList from outside misuse — usually by exposing methods rather than returning the list itself.

On the AP exam, ArrayList-field FRQs appear in library, inventory, and roster designs.

Library class

public class Library {
    private ArrayList<String> books;

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

    public void addBook(String title) {
        books.add(title);
    }

    public boolean removeBook(String title) {
        for (int i = 0; i < books.size(); i++) {
            if (books.get(i).equals(title)) {
                books.remove(i);
                return true;
            }
        }
        return false;
    }

    public boolean hasBook(String title) {
        for (String b : books) {
            if (b.equals(title)) return true;
        }
        return false;
    }

    public int getCount() { return books.size(); }
}

Why not return the ArrayList directly

If getBooks() returned books, callers could modify it directly — bypassing all the class's logic. Better to expose methods that do specific operations.

Standard operations

• add: append to the list.
• remove: find and delete.
• contains: search and report.
• count: report size.