sorting an array List [duplicate]

I think you should create a class to represent the elements in the list. For instance:

public class WordCount {
    public static final Comparator<WordCount> BY_COUNT;

    private static final Pattern PATTERN
            = Pattern.compile("\\s*([0-9]+)\\s+(.*)");

    public final int count;
    public final String word;

    public static WordCount parse(String s) {
        Matcher matcher = PATTERN.matcher(s);
        if (!matcher.matches()) {
            throw new IllegalArgumentException("Syntax error: " + s);
        }
        return new WordCount(
                Integer.parseInt(matcher.group(1)), matcher.group(2));
    }

    public WordCount(int count, String word) {
        this.count = count;
        this.word = word;
    }

    @Override
    public String toString() {
        return count + " " + word;
    }

    static {
        BY_COUNT = (WordCount o1, WordCount o2) -> {
            int r = Integer.compare(o1.count, o2.count);
            if (r == 0) {
                r = o1.word.compareTo(o2.word);
            }
            return r;
        };
    }
}

Your code would then become:

    List<WordCount> words = new ArrayList<>();  
    words.add(WordCount.parse("9 hello"));
    words.add(WordCount.parse("98 food"));
    words.add(WordCount.parse("105 cat"));
    words.add(WordCount.parse("2514 human"));
    words.add(WordCount.parse("3 pencil"));
    words.sort(WordCount.BY_COUNT.reversed());
    words.forEach((wc) -> {
        System.out.println(wc);
    });

With the following result:

2514 human
105 cat
98 food
9 hello
3 pencil

Use comporator to solve your problem like this

Add this code inside you class

  private static Comparator<String> ORDER_MYLIST = new Comparator<String>() {
            public int compare(String d, String d1) {
                int first = Integer.parseInt(d.split(" ")[0]);//since you have space 
                int second = Integer.parseInt(d1.split(" ")[0]);
                return second - first;//change the order if you want
            }
};

Add this code in your calling function

Collections.sort(words, ORDER_MYLIST);

Output:

[2514 human, 105 cat, 98 food, 9 hello, 3 pencil]

Will be as you expect.

This link will give you better understanding on how comporator works https://docs.oracle.com/javase/7/docs/api/java/util/Comparator.html

You need to have a custom comparator to satisfy your requirement. Java 8 solution:

List<String> words = new ArrayList<>();  
words.add("9 hello");
words.add("98 food");
words.add("105 cat");
words.add("2514 human");
words.add("3 pencil");

// Sort the existing list
words.sort(Comparator.comparing(s -> Integer.parseInt(s.split(" ")[0]), Comparator.reverseOrder()));

// To create new sorted list
List<String> sortedWords = words.stream()
            .sorted(Comparator.comparing(s -> Integer.parseInt(s.split(" ")[0]), Comparator.reverseOrder()))
            .collect(Collectors.toList());

What you've got is exactly lexicographical order because not numbers are compared but their digits alphabetically. If you want other behavior then you should consider implementing your own Comparator in which you'll parse the numbers.