【解決方法】書籍およびジャーナル オブジェクトを publicationlist 配列リストに追加する方法。

このプロジェクトには 4 つのクラスがありますが、私の本と雑誌がどのように publicationList に追加されるのかわかりません。 それらをリストに追加するにはどうすればよいですか。 これが私の4つのクラスです。

私が試したこと：

<pre>public class Database {
    private ArrayList<Publication> publicationList;   // An array list collection of publications 

    /**
     * Create a new database
     */
    public Database() {
        publicationList = new ArrayList<Publication>();
    }

    /**
     * Add a publication
     *
     * @param publication The publication to be added
     */
    public void addPublication(Publication publication) {
        if (publicationList.contains(publication)) {
            System.out.println("This publication has already been added to the list: " + publication);
        } else {
            publicationList.add(publication);
        }
    }

    /**
     * Get the total number of publications
     *
     * @return The total number of publications
     */
    public int getTotal() {
        return publicationList.size();
    }

    public ArrayList<Book> getBooksByAuthor(String authorName) {
        ArrayList<Book> authorsBooks = new ArrayList<Book>();
        for (Publication publication : publicationList) {
            if (publication instanceof Book) { 
                Book book = (Book) publication; // cast the publication to a book
                if (book.getAuthor().equals(authorName)) { // check if the author's name matches
                    authorsBooks.add(book); // add the book to the list
                }
            }
        }
        return authorsBooks;
    }

    public int getNumberOfJournals(int month, int year) {
        int count = 0;
        for (Publication publication : publicationList) {
            if (publication instanceof Journal) {
                Journal journal = (Journal) publication;
                if (journal.getMonth() == month && journal.getYear() == year) {
                    count++;
                }
            }
        }
        return count;
    }

    public void printList() {
        ArrayList<Book> books = new ArrayList<>();
        ArrayList<Journal> journals = new ArrayList<>();

        // filter publications by type
        for (Publication publication : publicationList) {
            if (publication instanceof Book) {
                books.add((Book) publication);
            } else if (publication instanceof Journal) {
                journals.add((Journal) publication);
            }
        }

        // sort publications by category and then by title within each category
        Comparator<Publication> categoryComparator = new Comparator<Publication>() {
                @Override
                public int compare(Publication p1, Publication p2) {
                    if (p1 instanceof Book && p2 instanceof Journal) {
                        return -1; // book before journal
                    } else if (p1 instanceof Journal && p2 instanceof Book) {
                        return 1; // journal after book
                    } else {
                        // same category, compare by title
                        return p1.getTitle().compareToIgnoreCase(p2.getTitle());
                    }
                }
            };

        Collections.sort(books, categoryComparator);
        Collections.sort(journals, categoryComparator);

        // print out the publications
        System.out.println("Books:");
        for (Publication publication : books) {
            System.out.println(publication);
        }

        System.out.println("Journals:");
        for (Publication publication : journals) {
            System.out.println(publication);
        }

        System.out.println("Total number of publications: " + getTotal());
    }
}

public class Publication {
    private String title;       // The title of the book
    private int year;           // The year when the book was published

    

    /**
     * Parameterized constructor for objects of class Publication
     * 
     * @param title     The title of the publication
     */
    public Publication(String title, int year) {
        this.title = title;
        this.year = year;
    }

    /**
     * Get the title of the publication
     *  
     * @return  The title of the publication
     */
    public String getTitle() {
        return title;
    }

    /**
     * Get the year when the journal was published
     *  
     * @return  The year when the journal was published
     */
    public int getYear()
    {
        return year;
    }

    public String toString() {
        return title + ", " + year;
    }

}

<pre>public class Journal extends Publication 
{   
    // The year and month when the journal was published
    private int month;

    /**
     * Create a journal. 
     * 
     * @param title     The title of the journal
     * @param month     The month when the journal was published
     * @param year      The year when the journal was published
     */
    public Journal(String title, int month, int year)
    {
        super(title, year);
        this.month = month;
    } 

    /**
     * Get the month when the journal was published
     *  
     * @return  The month when the journal was published
     */
    public int getMonth()
    {
        return month;
    }
    
    /**
     * Get the details of the journal
     *  
     * @return  The details of the journal, i.e. the title, year and month
     */
    public String toString()
    {
        return super.toString() + " (" + getMonthName(month) + ")";     
    }             
    
    /**
     * Check if the journal is the same as the given one.
     * 
     * @param obj The given object.
     * 
     * @return true  if the journal and the given one have the
     *               same title, year and month;
     *         false otherwise
     */
    public boolean equals(Object obj) {        
        if (this == obj) return true;
        if ( !(obj instanceof Journal) ) return false;
        
        var another = (Journal) obj;
        return this.getTitle().equals(another.getTitle()) &&
               this.month == another.month &&
               this.getYear() == another.getYear();
    }    
    
    /**
     * To get the name of a given month
     * 
     * @param month A given month
     * @return  The month's name
     */
    private String getMonthName(int month) {
        switch (month) {
            case 1: return "January";
            case 2: return "February";
            case 3: return "March";
            case 4: return "April";
            case 5: return "May";
            case 6: return "June";
            case 7: return "July";
            case 8: return "August";
            case 9: return "September";
            case 10: return "October";
            case 11: return "November";
            case 12: return "December";
            default: return "Unknown";
        }
    }    
}

<pre>public class Book extends Publication
{    
    private String author;      // The author of the book

    /**
     * Create a book. 
     * 
     * @param title     The title of the book.
     * @param author    The author of the book.
     * @param year      The year when the book was published.
     */
    public Book(String title, String author, int year)
    {
        super(title, year);
        this.author = author;
    }

    /**
     * Get the author of the book
     *  
     * @return  The author of the book
     */
    public String getAuthor()
    {
        return author;
    }

    /**
     * Get the details of the book
     *  
     * @return  The details of the book, i.e. the title, year and author
     */
    public String toString ()
    {
        return super.toString() + ", by " + author;     
    }         

    /**
     * Check if the book is the same as the given one.
     * 
     * @param obj The given object.
     * 
     * @return true  if the book and the given object have
     *               the same title, author and year
     *         false otherwise
     */
    public boolean equals(Object obj) {        
        if (obj == this) return true;
        if ( !(obj instanceof Book) )  return false;

        var another = (Book) obj;        
        return this.getTitle().equals(another.getTitle()) && 
        this.author.equals(another.author) &&
        this.getYear() == another.getYear();
    }            
}