Java
Data model
Set up the data model and collections.
The Catalog class and ArrayList
To manage multiple books you write a Catalog class. It contains an ArrayList<Book> and an addBook method that adds a new book.
import java.util.ArrayList;
class Catalog {
ArrayList<Book> books = new ArrayList<>();
void addBook(String title) {
books.add(new Book(title));
}
}
addBook takes a title, creates a new Book and adds it to the list. ArrayList is a dynamic array; you do not manage capacity. To print the list, System.out.println(cat.books) is enough; toString shows each book.
Print the list
System.out.println(cat.books) prints the whole list. The ArrayList's toString separates items with commas and wraps them in square brackets. Each Book's own toString is called.
cat.addBook("Suç ve Ceza");
cat.addBook("Sefiller");
System.out.println(cat.books);
// [[müsait] Suç ve Ceza, [müsait] Sefiller]
This lets you see the list contents without writing a separate loop. Notice how the toString design in the Book class pays off here; a good toString makes debugging easier.
Exercise Add two books and print them
Add a void addBook(String title) method to the Catalog class: create a new Book and add it to the books list. In main call cat.addBook("Suç ve Ceza") and cat.addBook("Sefiller"), then print cat.books.
Show example solution
// inside Catalog:
void addBook(String title) {
books.add(new Book(title));
}
// inside main:
cat.addBook("Suç ve Ceza");
cat.addBook("Sefiller");
System.out.println(cat.books);
Test yourself
-
Match each concept to its purpose
- ArrayList<Book>
- Book list
- addBook(String)
- Add book
- new Book(title)
- Create object
- books.add(...)
- Put in list
-
What does addBook("Suç ve Ceza") do?
- Removes a book from the list
- Borrows the book
- Creates a new Book and adds it to the list
- Prints the list
Show answer
Creates a new Book and adds it to the list — addBook creates a new Book object and adds it to the ArrayList.
-
Call addBook
Catalog cat = new Catalog();
cat.____("Sefiller");
Show answer
Catalog cat = new Catalog();
cat.addBook("Sefiller");
Next lesson: Business logic
