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Thread: What's wrong?

  1. #26
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    Default Re: What's wrong?

    The new class should look something like this?
    public class Author {
    	String authors;
     
    	public void Authorss(){
     
    	}
     
    }

  2. #27
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    Default Re: What's wrong?

    Something like that. I see your confidence in writing a basic class structure is low, because you don't understand them, and you probably haven't done much practicing. More practicing will improve your understanding and your confidence.

    If Authorss() was meant to be a constructor, remember that constructors have the same name as the class and don't have a return type. For the field 'authors', I would rename that lastName and add other fields for firstName and middleName or middleInitial (you choose). Then, as I suggested earlier, a field to collect all books written by the author, maybe an ArrayList publishedBooks. Again, you choose the collection and the name.

  3. #28
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    Default Re: What's wrong?

    Now I corrected:
    public class Book {
    	String books2;
     
    	public Book(){
    	}
    }

  4. #29
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    Default Re: What's wrong?

    This is my ArrayList. It's good?
    		String[] shelf;
    		shelf = new String[1];
    		shelf[0] = books2;
            System.out.println("Book on shelf 0: "+ shelf[0]);

  5. #30
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    Default Re: What's wrong?

    Now you're starting to get into the OOP part of this design, and you're floundering a bit, maybe even backsliding into using parallel arrays. You can use an array instance variable as the collection in which each Author object's books will be stored. In the real world, you wouldn't know how big the array will someday have to be, so a real ArrayList would probably be the collection of choice, but in this project, let's say an array of 5 elements is enough. In that case, you'd declare it something like:

    public class Author
    {
        Book[] books;
        String firstName;
        String lastName;
     
        // other instance variables
     
        // two-argument constructor that sets the author's name
        public Author( String firstName, String lastName )
        {
            // set the author's name
            this.firstName = firstName;
            this.lastName = lastName;
     
            // initialize the collection of books
            books = new Book[5];
     
            // continue the constructor as needed
     
        } // end constructor
     
        // other methods, getters, setters, etc.
     
    } // end class Author

  6. The Following User Says Thank You to GregBrannon For This Useful Post:

    Lukas (November 3rd, 2013)

  7. #31
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    Default Re: What's wrong?

    You said, that in this project 5 elements is enough. But can you say me, how to create as much as I want to insert Array elements?

  8. #32
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    Default Re: What's wrong?

    Of course. I speculated you had some confusion about or inability to use the actual ArrayList, so I steered away, but that would look like:
    public class Author
    {
        List<Book> books;
        String firstName;
        String lastName;
     
        // other instance variables
     
        // two-argument constructor that sets the author's name
        public Author( String firstName, String lastName )
        {
            // set the author's name
            this.firstName = firstName;
            this.lastName = lastName;
     
            // initialize the collection of books
            books = new ArrayList<>();
     
            // continue the constructor as needed
     
        } // end constructor
     
        // other methods, getters, setters, etc.
     
    } // end class Author
    Note: The above construction will work in Java 7 because of its type inference but may require minor adjustments for earlier versions.

  9. The Following User Says Thank You to GregBrannon For This Useful Post:

    Lukas (November 3rd, 2013)

  10. #33
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    Default Re: What's wrong?

    And in Book class write:
    public class Book
    {
        Book[] books;
        String bookName;
     
        public Book(String bookName)
        {
            this.bookName = bookName;
        } 
    }
    Or change something or what?

  11. #34
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    Default Re: What's wrong?

    Except that Book doesn't need an array called books, at least I don't think so. How would that array be used? What purpose would it serve? Other than that, it looks fine.

    I assume you'll add a getter and setter for the bookName, and it may grow to include other instance variables with their getters and setters, but that's a reasonable start.

  12. #35
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    Default Re: What's wrong?

    Now good?
    public class Book
    {
        String bookName;
     
        public Book(String bookName)
        {
            this.bookName = bookName;
        } 
    }
    And how to use class Author and class Book in Class Authors2. When I write in class Authors2 this:
    System.out.println("Please write the author name: ");
    authors = scan.nextLine();
    And how can I instead of authors change to firstName? When I change authors to firstName, the program don't understand what is this..

  13. #36
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    Default Re: What's wrong?

    Here's an example of how it could look all put together. Notice that because all classes have been included in a single file called LibraryManager.java, only the top-level class with the main() method can be public. The other classes could be public if they were stored in their own files, but they wouldn't have to be. You need to make progress from here. I've mentioned getter and setter methods several times, but you've not added any to the skeleton classes you've constructed. I added one to the Author class so you could work from an example, and there are more for you to write.
    import java.util.Scanner;
    import java.util.List;
    import java.util.ArrayList;
     
    public class LibraryManager
    {
        Scanner scan;
     
        // constructor and currently drives the program
        public LibraryManager()
        {
            scan = new Scanner( System.in );
        }
     
        public static void main( String[] args )
        {
            // create a LibraryManager instance for demo use
            LibraryManager libraryManager = new LibraryManager();
     
            // get the author's name and . . . 
            String authorsName = libraryManager.getAuthorsName();
     
            // . . . create an author instance
            Author author = new Author( authorsName, "Blank" );
     
            // show how to use the Author's getter, getAuthorsWholeName
            System.out.println( "The Author's name is: " 
                + author.getAuthorsWholeName() );
     
        } // end method main()
     
        // method getAuthorsName() asks the user for the author's name and
        // returns the user's input. no error checking is done.
        private String getAuthorsName()
        {
            System.out.println("Please write the author's name: ");
            String authors = scan.nextLine();
     
            return authors;
     
        } // end method getAuthorsName()
     
    } // end class LibraryManager
     
     
    class Author
    {
        List<Book> books;
        String firstName;
        String lastName;
     
        // other instance variables
     
        // two-argument constructor that sets the author's name
        public Author( String firstName, String lastName )
        {
            // set the author's name
            this.firstName = firstName;
            this.lastName = lastName;
     
            // initialize the collection of books
            books = new ArrayList<>();
     
            // continue the constructor as needed
     
        } // end constructor
     
        // other methods, getters, setters, etc.
        public String getAuthorsWholeName()
        {
            return firstName + " " + lastName;
     
        } // end method getAuthorsWholeName()
     
    } // end class Author
     
    class Book
    {
        String bookName;
     
        // constructor that specifies the book's name
        public Book(String bookName)
        {
            this.bookName = bookName;
        }
     
    } // end class Book
    Here's an example run:
    Please write the author's name:
    Lukas
    The Author's name is: Lukas Blank

  14. The Following User Says Thank You to GregBrannon For This Useful Post:

    Lukas (November 3rd, 2013)

  15. #37
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    Default Re: What's wrong?

    Thank you too much
    I try to do something:
    import java.util.Scanner;
    import java.util.List;
    import java.util.ArrayList;
     
    public class LibraryManager
    {
        Scanner scan;
     
    	// constructor and currently drives the program
        public LibraryManager()
        {
            scan = new Scanner( System.in );
        }
        public static void main( String[] args)
        {
            // create a LibraryManager instance for demo use
            LibraryManager libraryManager = new LibraryManager();
     
            // get the author's name and . . . 
            String authorsName = libraryManager.getAuthorsName(); 
            String authorsSurname = libraryManager.getAuthorsSurname();
            String getAuthorshowbooks = libraryManager.getAuthorshowbooks(); 
            // . . . create an author instance
            Author author = new Author( authorsName, authorsSurname );
     
            // show how to use the Author's getter, getAuthorsWholeName
            System.out.println( "The Author's name and surname is: " 
                + author.getAuthorsWholeName() );
     
        } // end method main()
     
        // method getAuthorsName() asks the user for the author's name and
        // returns the user's input. no error checking is done.
        private String getAuthorsName()
        {
            System.out.println("Please write the author's name: ");
            String authors = scan.nextLine();
            return authors;
     
        } // end method getAuthorsName()
    	private String getAuthorsSurname()
    	  {
            System.out.println("Please write the author's surname: ");
            String authors = scan.nextLine();
     
            return authors;
     
        } // end method getAuthorsName()
    	private String getAuthorshowbooks()
    	  {
          System.out.println("Please write how many author's books you want to insert: ");
          String authors = scan.nextLine();
     
          return authors;
     
      } 
     
    } // end class LibraryManager
    class Author
    {
        List<Book> books;
        String firstName;
        String lastName;
     
        // other instance variables
     
        // two-argument constructor that sets the author's name
        public Author( String firstName, String lastName )
        {
            // set the author's name
            this.firstName = firstName;
            this.lastName = lastName;
     
            // initialize the collection of books
            books = new ArrayList<>();
     
            // continue the constructor as needed
     
        } // end constructor
     
        // other methods, getters, setters, etc.
        public String getAuthorsWholeName()
        {
            return firstName + " " + lastName;
     
        } // end method getAuthorsWholeName()
     
    } // end class Author
     
    class Book
    {
        String bookName;
     
        // constructor that specifies the book's name
        public Book(String bookName)
        {
            this.bookName = bookName;
        }
     
    } // end class Book
    But all time I don't understand one thing. I write how many books I want to insert, and when I'm writing the books, my result are the last book or error...
    But now, I don't understand at all how to create this...

  16. #38
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    Default Re: What's wrong?

    You've made some progress, but if you want to get the user's desired NUMBER of something, then you'll need to either scan for a NUMBER or parse the scanned String into a NUMBER. This is basic stuff you should have some concept of, even if you don't know how exactly to do it.

  17. #39
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    Default Re: What's wrong?

    I don't know.. What can I do more..
    private String getAuthorshowbooks()
    	  {
          System.out.println("Write how many author's books you want to insert: ");
          how = scan.nextLine();
     
    	return how;
      } 
    	private String getAuthorsbooks()
    		{
    			System.out.println("Write the author's books: " + how);
    			String authors = scan.nextLine();
     
    			return authors;
    		}
    I don't know.. What can I do more.. I'm confused in my program.
    In the previous program I was able to write those books .. But the program give me the last book.. And now I do not know .. Somehow differently here..

  18. #40
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    Default Re: What's wrong?

    GregBrannon help... I do not know how to convert the scanned line in number... Write me that code if you can... Then I will understand what's going on.

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