Iterate and Alphabetize ArrayList of Strings by Last Word in Each String

Question

I've tried numerous solutions and am really struggling here.

I have an arraylist full of strings ranging in length.

I need to sort the strings alphabetically by the last word in each string.

Some strings are entered as "Unknown" while others are multiple words.

Example:

static List<String> authors = new ArrayList<>();
authors.add("Unknown");
authors.add("Hodor");
authors.add("Jon Snow");
authors.add("Sir Jamie Lannister");
sort(authors);
System.out.println(authors);

Should return:

Hodor
Sir Jamie Lannister
Jon Snow
Unknown    

How can i iterate this list sorting by the last name / word in each string?

Thanks immensely for any suggestions. I Will continue to google in the meantime.

Answer 1

You can provide a custom Comparator<String> and call Collections.sort(List<T>, Comparator<T>) , like

List<String> authors = new ArrayList<>(Arrays.asList("Unknown", "Hodor", "Jon Snow",
        "Sir Jamie Lannister"));
Collections.sort(authors, new Comparator<String>() {
    @Override
    public int compare(String o1, String o2) {
        String[] left = o1.split("\\s+");
        String[] right = o2.split("\\s+");
        return left[left.length - 1].compareTo(right[right.length - 1]);
    }
});
System.out.println(authors);

Which outputs (as requested)

[Hodor, Sir Jamie Lannister, Jon Snow, Unknown]

Answer 2

in Java 8, this might work

public void sort(List<String> authors) {
    Collections.sort((l, r) -> lastWord(l).compareTo(lastWord(r); )
}

public String lastWord(String str) {
    return str.substring(str.lastIndexOf(' ') + 1);
}