Everything works...I don't know what codegym wants from me..

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Everything works...I don't know what codegym wants from me...I'm confused..

1. Create a public static class MarkTwainBook that inherits Book. Name of the author [Mark Twain].
The constructor parameter is the book title.
2. Implement all the abstract methods in the MarkTwainBook class.
3. Change the return type of the getBook method to make it more appropriate.
4. In a similar manner, create the AgathaChristieBook class. Name of the author [Agatha Christie].
5. In the Book class, implement the getOutputByBookType method so that it returns:
5.1. agathaChristieOutput for books written by Agatha Christie;
5.2. markTwainOutput for books written by Mark Twain.

Requirements:

The Solution class must contain the public static MarkTwainBook class.
The MarkTwainBook class must be a descendant of the Book class.
The MarkTwainBook class must correctly implement a constructor with one String parameter (book title).
The MarkTwainBook class constructor should call the constructor of the parent class (Book) with the argument "Mark Twain".
The getBook method in the MarkTwainBook class must have the MarkTwainBook return type and return the current object.
The Solution class must contain the public static AgathaChristieBook class.
The AgathaChristieBook class must be a descendant of the Book class.
The AgathaChristieBook class must correctly implement a constructor with one String parameter (book title).
The AgathaChristieBook class constructor should call the constructor of the parent class (Book) with the argument "Agatha Christie".
The getBook method in the AgathaChristieBook class must have the AgathaChristieBook return type and return the current object.
The getTitle method in the AgathaChristieBook and MarkTwainBook classes should return the title of a specific book.
The getOutputByBookType method must return the correct string for AgathaChristieBook objects.
The getOutputByBookType method must return the correct string for MarkTwainBook objects.
The MarkTwainBook class must have a String field title (book title).
The AgathaChristieBook class must have a String field title (book title).

package com.codegym.task.task15.task1504; import java.util.LinkedList; import java.util.List; /* OOP: Books */ public class Solution { public static void main(String[] args) { List<Book> books = new LinkedList<Book>(); books.add(new MarkTwainBook("Tom Sawyer")); books.add(new AgathaChristieBook("Hercule Poirot")); System.out.println(books); } abstract static class Book { private String author; public Book(String author) { this.author = author; } public abstract Book getBook(); public abstract String getTitle(); private String getOutputByBookType() { String agathaChristieOutput = MarkTwainBook.author + ": " + getBook().getTitle() + " is a detective"; String markTwainOutput = getBook().getTitle() + " was written by " + AgathaChristieBook.author; String output = "output"; if(getTitle().equals(MarkTwainBook.title)){ output = markTwainOutput; } else if (getTitle().equals(AgathaChristieBook.title)){ output = agathaChristieOutput; } return output; } public String toString() { return getOutputByBookType(); } } public static class MarkTwainBook extends Book{ public static String author = "Mark Twain"; public static String title; public MarkTwainBook(String title){ super(title); this.title = title; } public MarkTwainBook getBook(){ return this; } public String getTitle(){ return MarkTwainBook.title; } } public static class AgathaChristieBook extends Book{ public static String author = "Agatha Christie"; public static String title; public AgathaChristieBook(String title){ super(title); AgathaChristieBook.title = title; } public AgathaChristieBook getBook(){ return this; } public String getTitle(){ return AgathaChristieBook.title; } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

13 December 2020, 22:42

#1 using static fields, unless you have a specific reason to, is usually wrong. In this task, each book should have a unique title, but static variables are class wide and thus not unique. #2 The book class already has an author field that is set with the constructor. In both the sub classes the constructor passes the title to that constructor instead of the author. This needs to be changed. That also means that the sub classes do not need an author field

Vitalina

Level 20 , Poland

14 December 2020, 15:24

But how can I write two constructors with String parameter??? It looks like this: public MarkTwainBook(String author){ super(author); this.author = author; } public MarkTwainBook(String title){ super(title); this.title = title; }

Guadalupe Gagnon

Level 37 , Tampa, United States

14 December 2020, 15:35

The task requires only 1 constructor per class. The author field inside the sub classes (lines 52 and 70) are both being used incorrectly. Because the book classes are for the author, using static variables for them is acceptable in this case as the names shouldn't change. However, you still need to pass the author names up to the super constructor to make the (super) Book class valid. Basically the 2 constructors that you shared both have one piece of the puzzle correct and one piece incorrect. Combine them into one constructor with the correct item each. **Tip: the constructor's job is to ensure the object is valid. In this task, to make a valid object the author field from the book class needs to have a value and the title field from the 2 derived classes need to have a value.

Vitalina

Level 20 , Poland

14 December 2020, 17:10

ok. So I wrote something like this: public static class MarkTwainBook extends Book { public static String author; public String title; public MarkTwainBook(String title) { super(author); author = "Mark Twain"; this.title = title; } But when I'm running a String getOutputByBookType() method - the author is null:( Sorry, I don't know why it is so complicated for me to understand. I will be very thankful for help!

Guadalupe Gagnon

Level 37 , Tampa, United States

14 December 2020, 17:13

solution

In that code author has no value (is null) when it is passed to the super constructor because you provide a value for author afterwards. This won't work. You need to set author to the correct value on the line you declare it, or remove it completely and just pass a string literal to the super constructor.

Vitalina

Level 20 , Poland

14 December 2020, 17:15

I wrote: public static class MarkTwainBook extends Book { public static String author = "Mark Twain"; public String title; public MarkTwainBook(String title) { super(author); author = author; this.title = title; } And it works. Thank you very much for help and your patience!

Guadalupe Gagnon

Level 37 , Tampa, United States

14 December 2020, 17:19

You can remove the line

author = author;

This does nothing meaningful. It is just setting the value of author to the value it currently is.

Misiu

Level 41 , Gdansk, Poland

13 December 2020, 22:41

"The MarkTwainBook class constructor should call the constructor of the parent class (Book) with the argument "Mark Twain"." There is something to correct in lines 31, 32.