Sorting arraylist of string arrays Java

Question

I have a program that takes a word and a text file dictionary, and searches the dictionary for combinations of words that equal (are anagrams of) the given word.

I end up with an Arraylist of String arrays, each array is a solution containing the words it used, and the Arraylist is all solutions.

I then iterate over the arraylist and sort the arrays as:

List<String> list = Arrays.asList(array);
list.sort(Comparator.comparing(String::length).reversed().thenComparing(String::compareTo));

which sorts first by word length (descending) and then uses alphabetical as a tie breaker for equal length words.

I now have the individual arrays sorted but i'm trying to sort them within the arraylist by certain rules:

• by ascending number of words
• for arrays that contain equal number of words, and all words are of same length, the arrays are alphabetically sorted.
• equal number of words, but differing lengths: longest non-equal length first. Eg if a[0] length == b[0] length but b[1] length>a[1] length, b comes first.

They are already stored by ascending number of words as single word solutions are found first, then 2 word and so on, being appended to the arraylist.

Now as the arrays are in descending word length order too after sorting, i'm thinking there must be a straightforward Comparator to achieve the above but i'm struggling to do it.

Answer 1

First, there is no need to convert the array to List in order to sort.

Second, you should use thenComparing(Comparator.naturalOrder()) instead of thenComparing(String::compareTo) , as that will use a singleton Comparator , rather than creating a new Comparator delegating to the method reference.

As for your question, I don't think there exists a Comparator for that, so just create your own. The building of a compound Comparator using thenComparing() is nice, but not always the right way to go.

So, your code could be (assuming I got your sort criteria right) :

List<String[]> solutions = /* code here */;

// First, sort each individual solution (array)
for (String[] solution : solutions) {
    Arrays.sort(solution, Comparator.comparing(String::length)
                                    .reversed()
                                    .thenComparing(Comparator.naturalOrder()));
}

// Second, sort the solutions (list)
solutions.sort((solution1, solution2) -> {
        // 1) By number of words (ascending)
        int cmp = Integer.compare(solution1.length, solution2.length);
        // 2) By length of word (descending)
        for (int i = 0; cmp == 0 && i < solution1.length; i++)
            cmp = Integer.compare(solution2[i].length(), solution1[i].length());
        // 3) Alphabetically (ascending)
        for (int i = 0; cmp == 0 && i < solution1.length; i++)
            cmp = solution1[i].compareTo(solution2[i]);
        return cmp;
});