(Java) Loading from a text file to a Arraylist

Question

For this program I need to read in a list of data for a book (Title, Author, Price) from a text file to an arraylist in a separate class (Book). Ill be honest I just using Classes as objects within Java is just one of the things I cannot wrap my head around, and I dont have much experience with ArrayLists.

public void loadBook(String fn) throws IOException{     
    ArrayList<Book> books = new ArrayList<Book>();
    Scanner infile = new Scanner(new InputStreamReader (new FileInputStream(fn)));
    int num = infile.nextInt();
    infile.nextLine();
    for (int i=0; i<num; i++) {
        String name = infile.nextLine();
        String author = infile.nextLine();
        Double price = infile.nextDouble();
        Book c = new Book (name, author, price);
        books.add(c);
    }
    infile.close();
    }

And this is the code currently in the Book class.

public class Book extends Model {

public Book(String name, String author, Double price) {
    String Name = name;
    String Author = author;
    Double Price = price;
}

And the file 'fn' contains this:

3
name
author
10.00

But loadBook still throws an error when reading in a file :@

Any help would be appreciated, thank you!!

"loadBook throws an error" --> Always include the complete error message in this type of questions. — jlordo
– jlordo, Commented Feb 13, 2013 at 16:04
I tried really hard to add the Stack trace, but for some reason StackOverflow had a problem with my code after and wouldnt let me save the edit, sorry — Kamon241
– Kamon241, Commented Feb 13, 2013 at 16:10

jlordo · Accepted Answer · 2013-02-13 16:08:41Z

3

With this input:

3
name
author
10.00

This code

int num = infile.nextInt();
infile.nextLine();
for (int i=0; i<num; i++) {
    String name = infile.nextLine();
    String author = infile.nextLine();
    Double price = infile.nextDouble();
    Book c = new Book (name, author, price);
    books.add(c);
 }

will set num to 3 and therefore execute the for loop 3 times. In each iteration the method nextLine() is called twice and nextDouble() once. But there are only 3 more lines in the file, so you are calling nextLine() too often. Try changing your input to

1      <-- number of listed books, not lines.
name
author
10.00

answered Feb 13, 2013 at 16:08

jlordo

37.9k7 gold badges63 silver badges84 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Kamon241 Over a year ago

Beautiful, Ill give it a run now

Joop Eggen Over a year ago

You could also leave out the number and test with if (!infile.hasNextLine()) break;

Kamon241 Over a year ago

IT WORKS!!, You may have just saved me hours. Thank you so much (Apperently I have to wait 2 mins until your the correct answer)

lejadina · Accepted Answer · 2013-02-13 16:09:35Z

1

Try make sure your text file is in your package in eclipse with .txt extention

//see what your default path is
System.out.println(System.getProperty("user.dir"));

//then use this code as continuation to the default path...for example if your path leads to your working directory
Scanner in = new Scanner(new FileInputStream("src/package_name/filename.txt"));

answered Feb 13, 2013 at 16:09

lejadina

315 bronze badges

1 Comment

Kamon241 Over a year ago

Yeah, the file is one of the few things with this code that didn't have a mystery problem. Cheers anyway tho

Collectives™ on Stack Overflow

(Java) Loading from a text file to a Arraylist

2 Answers 2

3 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related