Java sort list with streams first by length then alphabetically

Question

I can sort already by the description length, but how can I alphabetically sort two Article if two of them have the same length? (if the description of two articles has the same length, then the sorting should be alphabetical).

   public List<Article> sortAsc() {
    removeNull();
    return articles.stream()
            .sorted(Comparator.comparingInt(a -> a.getDescription().length()))
            .collect(Collectors.toList());
}




public class ComparatorAppController implements Comparator<String> {

/***
 * compare each element
 * @param o1
 * @param o2
 * @return
 */
public int compare(String o1, String o2) {
    // check length in one direction
    if (o1.length() > o2.length()) {
        return 1;
    }
    // check length in the other direction
    else if (o1.length() < o2.length()) {
        return -1;
    }
    // if same alphabetical order
    return o1.compareTo(o2);
}

}

How can I use my Comparator for this situation? Or should I change it to something else?

dani-vta · Accepted Answer · 2022-05-26 08:01:48Z

2

If you need to sort first by description length and then by description (alphabetical order), then your first comparison is fine but you also need to add a second comparison by description.

You can stack a second comparison by using the method thenComparing(). It will perform the second comparison only for elements with same length. There is no need to implement a custom Comparator for this scenario.

public List<Article> sortAsc() {
    removeNull();
    return articles.stream()
            .sorted(Comparator.comparingInt((Article a) -> a.getDescription().length())
                .thenComparing(Article::getDescription))
            .collect(Collectors.toList());
}

edited May 26, 2022 at 8:01

answered May 26, 2022 at 7:55

dani-vta

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Comments

Panagiotis Bougioukos · Accepted Answer · 2022-05-26 07:46:57Z

2

Your custom comparator seems good. However in the sorted method of streams you use another comparator.

This is how you can pluggin your custom comparator considering it is in the same class with the following block of code.

  return articles.stream()
            .sorted(this::compare)
            .collect(Collectors.toList());

answered May 26, 2022 at 7:46

Panagiotis Bougioukos

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Comments

azro · Accepted Answer · 2022-05-26 07:56:39Z

2

Use Comparator.comparing(KeyExtractor,Comparator)

public List<Article> sortAsc() {
    removeNull();
    return articles.stream()
            .sorted(Comparator.comparing(a -> a.getDescription(), new ComparatorAppController()))
            .collect(Collectors.toList());
}

Or define all the criterias with some thenComparing*

public static List<Article> sortAsc() {
    return articles.stream()
            .sorted(Comparator.<Article>comparingInt(a -> a.getDescription().length())
                    .thenComparing(Article::getDescription))
            .collect(Collectors.toList());
}

edited May 26, 2022 at 7:56

answered May 26, 2022 at 7:48

azro

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Comments

Sayan Bhattacharya · Accepted Answer · 2022-05-26 07:56:00Z

1

Why you need to sort in stream ,you can simply call 'sort' method for your list.

articles.sort(new ComparatorAppController());

You can add n numbers of comparator in sort method. eg:-

articles.sort(new ComparatorAppController().thenComparing(new SomeOtherComparing()));

You can also use thenComparing in the stream also.

articles.stream()
            .sorted(Comparator.comparingInt(a -> a.getDescription().length()).thenComparing(new SomeOtherComparing()))
            .collect(Collectors.toList());

answered May 26, 2022 at 7:56

Sayan Bhattacharya

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Comments

Bohemian · Accepted Answer · 2022-05-26 07:57:16Z

1

Delete your comparator and build one using comparing() and thenComparing():

articles.stream()
  .sorted(Comparator.comparing(a -> a.getDescription().length())
                    .thenComparing(Article::getDescription))
        .collect(Collectors.toList());

answered May 26, 2022 at 7:57

Bohemian♦

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