java arraylist class program [closed]

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im confused with a question which i was given, which is about bookshelf program. I have to create 2 classes called Book and BookShelf

I have more or less completed the Book class which contains these variables (id, author and title) with ( get, set , toString and constructors methods)

However for the BookShelf class, I am kind of clueless whether what i have done is correct

Here is what I am supposed to do at the BookShelf class

• Create an addBook method, it takes in book object as input and adds the object into the bookshelf

• returnBooks method, no parameter / arguments needed just return an arraylist of books in order

• returnAuthorBooks, takes in author as input and returns an arraylist of books by the author

This is the code that i have done

import java.util.ArrayList; 
import java.util.Collections;
public class BookShelf {
 ArrayList<Book> listOfBooks = new ArrayList<Book>();
 public void addBook(Book getTitle){
 listOfBooks.add(getTitle);
 }
 public ArrayList<Book> returnBooks(){
 ArrayList myBook = new ArrayList();
 Collections.sort(myBook);
 return myBook;
 }
 public ArrayList<Book> returnAuthor(Book author){
 for (Book books : listOfBooks){
 if (author.getAuthor() == books.getTitle()){
 return listOfBooks;
 }
 }
 return null;
 }
}

Would like to clarify if there is any mistake here as for some reason i get the feeling that i have done something incorrect

• Mark Rotteveel: This is borderline off-topic as it would be more suitable for codereview.stackexchange.com However take a close look at returnAuthor. For one, why are you passing a Book and not just a String with the author name, don't use == for string equality check, and you are returning the entire book list, not just the list of books by that author. Returning null is a bad habit as well.
• Eran: @MarkRotteveel I'm not sure about that. codereview is for review of code that works. I'm afraid this code doesn't qualify.
• Mark Rotteveel: @Eran You might be right, but in the absence of actual specific questions it sounds more like a request for code review; anyway, it is also off topic here.
• OneCricketeer: To make you code easier to read, you could name your method parameters book. For example, a variable name of author makes someone reading the code think that may be a string or an Author class. Similarly for getTitle, that's more a method name than a variable name, but don't name it just title because it's a Book object.

Answer 1

Your returnBooks method returns an empty List. You should change

ArrayList myBook = new ArrayList();

to

ArrayList<Book> myBook = new ArrayList(listOfBooks);

In order to return a full sorted list.

Your returnAuthor method has several problems :

1. It should take an author as input (I don't know if it should be a String or whether there is an Author class).
2. You compare the book's authors with == instead of equals (see this question).
3. You return the entire list of books if you find a book with the author you are looking for. You should only return the books of that author.

• Eran: @Turing85 Thanks for the edit, but I don't think books' was a typo (I'm not a native English speaker, and it has been many years since I finished learning English in high school, so I may be wrong). When you want to add 's (I forgot the name of that suffix) to a word that already ends with s (as books), you just add '. Your fix would be correct if I wanted to say the OP was comparing the authors of a single book. I wanted to say OP was comparing the authors of multiple books.
• Turing85: actually, I just changed an ` to an ', you ar probably right (my original intend was to add the link to the String comparison question).