Code-Alongs for Sprint 6

Code-Along: Building a Library Management System

In this code-along, we'll build a library management system that demonstrates the principles of encapsulation, polymorphism, and the use of generics.

Project Structure

The library system will include the following components:

• A LibraryItem interface that defines common behaviors
• Abstract Item class that implements the interface
• Concrete classes: Book, DVD, and Magazine
• A generic Catalog<T extends LibraryItem> class to manage collections of items
• A Library class that uses encapsulation to protect its data

Key Learning Points

• Implementing interfaces for polymorphic behavior
• Using encapsulation to protect library item data
• Creating a generic catalog to handle different types of items
• Applying primitive wrapper classes where appropriate

Getting Started

1. Create a new Java project in your IDE
2. Set up the package structure: com.bloomtech.library
3. Follow the implementation steps below

package com.bloomtech.library;

public interface LibraryItem {
    String getTitle();
    String getUniqueId();
    boolean isAvailable();
    void checkOut();
    void checkIn();
}

package com.bloomtech.library;

public abstract class Item implements LibraryItem {
    private final String uniqueId;
    private final String title;
    private boolean available;
    
    public Item(String uniqueId, String title) {
        this.uniqueId = uniqueId;
        this.title = title;
        this.available = true;
    }
    
    @Override
    public String getUniqueId() {
        return uniqueId;
    }
    
    @Override
    public String getTitle() {
        return title;
    }
    
    @Override
    public boolean isAvailable() {
        return available;
    }
    
    @Override
    public void checkOut() {
        if (available) {
            available = false;
        } else {
            throw new IllegalStateException("Item is already checked out");
        }
    }
    
    @Override
    public void checkIn() {
        available = true;
    }
}

package com.bloomtech.library;

// Book class
public class Book extends Item {
    private final String author;
    private final String isbn;
    private final Integer pageCount;
    
    public Book(String uniqueId, String title, String author, String isbn, int pageCount) {
        super(uniqueId, title);
        this.author = author;
        this.isbn = isbn;
        this.pageCount = pageCount;
    }
    
    public String getAuthor() {
        return author;
    }
    
    public String getIsbn() {
        return isbn;
    }
    
    public Integer getPageCount() {
        return pageCount;
    }
}

// DVD class
public class DVD extends Item {
    private final String director;
    private final Integer runtime;
    
    public DVD(String uniqueId, String title, String director, int runtime) {
        super(uniqueId, title);
        this.director = director;
        this.runtime = runtime;
    }
    
    public String getDirector() {
        return director;
    }
    
    public Integer getRuntime() {
        return runtime;
    }
}

package com.bloomtech.library;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Catalog<T extends LibraryItem> {
    private final Map<String, T> items;
    
    public Catalog() {
        this.items = new HashMap<>();
    }
    
    public void addItem(T item) {
        items.put(item.getUniqueId(), item);
    }
    
    public T findById(String id) {
        return items.get(id);
    }
    
    public List<T> findAvailableItems() {
        List<T> availableItems = new ArrayList<>();
        
        for (T item : items.values()) {
            if (item.isAvailable()) {
                availableItems.add(item);
            }
        }
        
        return availableItems;
    }
    
    public int getCount() {
        return items.size();
    }
}

package com.bloomtech.library;

import java.util.List;

public class Library {
    private final Catalog<Book> bookCatalog;
    private final Catalog<DVD> dvdCatalog;
    
    public Library() {
        this.bookCatalog = new Catalog<>();
        this.dvdCatalog = new Catalog<>();
    }
    
    public void addBook(Book book) {
        bookCatalog.addItem(book);
    }
    
    public void addDVD(DVD dvd) {
        dvdCatalog.addItem(dvd);
    }
    
    public Book findBookById(String id) {
        return bookCatalog.findById(id);
    }
    
    public DVD findDVDById(String id) {
        return dvdCatalog.findById(id);
    }
    
    public List<Book> findAvailableBooks() {
        return bookCatalog.findAvailableItems();
    }
    
    public List<DVD> findAvailableDVDs() {
        return dvdCatalog.findAvailableItems();
    }
    
    public void checkOutItem(LibraryItem item) {
        item.checkOut();
    }
    
    public void returnItem(LibraryItem item) {
        item.checkIn();
    }
    
    public int getTotalItemCount() {
        return bookCatalog.getCount() + dvdCatalog.getCount();
    }
}

package com.bloomtech.library;

public class LibraryDemo {
    public static void main(String[] args) {
        // Create a library
        Library library = new Library();
        
        // Add some books
        Book book1 = new Book("B001", "Effective Java", "Joshua Bloch", "978-0134685991", 416);
        Book book2 = new Book("B002", "Clean Code", "Robert C. Martin", "978-0132350884", 464);
        
        // Add some DVDs
        DVD dvd1 = new DVD("D001", "The Matrix", "Wachowski Sisters", 136);
        DVD dvd2 = new DVD("D002", "Inception", "Christopher Nolan", 148);
        
        // Add items to library
        library.addBook(book1);
        library.addBook(book2);
        library.addDVD(dvd1);
        library.addDVD(dvd2);
        
        // Display total items
        System.out.println("Total items in library: " + library.getTotalItemCount());
        
        // Check out an item
        System.out.println("\\nChecking out " + book1.getTitle());
        library.checkOutItem(book1);
        
        // Find available books
        System.out.println("\\nAvailable books:");
        for (Book book : library.findAvailableBooks()) {
            System.out.println(" - " + book.getTitle() + " by " + book.getAuthor());
        }
        
        // Try to find an item by ID
        String searchId = "D001";
        DVD foundDVD = library.findDVDById(searchId);
        if (foundDVD != null) {
            System.out.println("\\nFound DVD: " + foundDVD.getTitle() + " directed by " + foundDVD.getDirector());
            System.out.println("Runtime: " + foundDVD.getRuntime() + " minutes");
        }
        
        // Return an item
        System.out.println("\\nReturning " + book1.getTitle());
        library.returnItem(book1);
        
        // Check available books again
        System.out.println("\\nAvailable books after return:");
        for (Book book : library.findAvailableBooks()) {
            System.out.println(" - " + book.getTitle() + " by " + book.getAuthor());
        }
    }
}

Practice: Extend the System

Try extending the library system with:

• A Magazine class extending Item
• A Borrower class to represent library users
• Functionality to track which borrower has checked out which items