CODEWITHSUNDEEP
javalinked-list
Lorenzo
Lorenzo

Reputation: 47

Wrong sort of linked list

I have a linked list of objects (Books, which fields are title, author and others). Why this implementation of sorting by title gives wrong results?

import java.util.*;

public class sort
{
    public static void main(String[] args)
    {
        LinkedList<Book> l = new LinkedList<>();
        l.add(new Book("Vargas Fred", "Il morso della reclusa"));
        l.add(new Book("Postorino Rossella", "Le assaggiatrici"));
        l.add(new Book("Bythell Shaun", "Una vita da libraio"));
        l.add(new Book("Simenon Georges", "Il fondo della bottiglia"));



        Collections.sort(l, new Comparator<Book>() {
            @Override
            public int compare(Book o1, Book o2) {
                return o1.title.length() - o2.title.length();
            }
        });


        for(Book i : l)
        {
            System.out.println(i.title);
        }
    }
}

Expected: - Il fondo della bottiglia - Il morso della reclusa - Le assaggiatrici - Una vita da libraio

Result: - Le assaggiatrici - Una vita da libraio - Il morso della reclusa - Il fondo della bottiglia

Upvotes: 0

Views: 77

Answers (2)

fmatar
fmatar

Reputation: 3470

This should solve your problem. I'm using lambdas and JDK 8

Here's an example Book class:

public class Book {

  final String author;
  final String title;


  public Book(String author, String title) {
    this.author = author;
    this.title = title;

  }

  public String title() {
    return this.title;
  }

  public String author() {
    return this.author;
  }
}

Now the comparison happens here: 

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class SortTest {

  public static void main(String... args) {
    List<Book> l = new ArrayList<>();
    l.add(new Book("Vargas Fred", "Il morso della reclusa"));
    l.add(new Book("Postorino Rossella", "Le assaggiatrici"));
    l.add(new Book("Bythell Shaun", "Una vita da libraio"));
    l.add(new Book("Simenon Georges", "Il fondo della bottiglia"));

    Collections.sort(l, Comparator.comparing(Book::title));
    l.forEach(book -> System.out.println(book.title));
  }

}

Upvotes: 0

clinomaniac
clinomaniac

Reputation: 2218

If you want to sort the books by Alphabetical order rather than the length of the title, you need to use this:

return o1.title.compareTo(o2.title);

Upvotes: 2

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