sorting strings in Java based on substrings

Question

I have a list of strings def123, abc999, zzz000, abc123, zzz111. I want the list sorted such that first three characters are sorted in ascendng order and next three in descending. So the output should be abc999, abc123, def123, zzz111,zzz000 Is this possible?

Answer 1

Other answers have suggested you implement Comparator. That's no longer necessary with recent utility methods added to the interface in Java 8:

list.sort(Comparator
    .comparing(s -> s.substring(0, 3))
    .thenComparing(s -> s.subtring(3, 6), Comparator.reverseOrder()));

Also note that List now has a sort method.

Answer 2

Yes, it is possible. You will have to write your own Comparator. Here's a tutorial to get you started https://www.tutorialspoint.com//java/java_using_comparator.htm

Answer 3

Break the strings into two substrings and then sort using comparator. Something like this: Demo

List<String> list = Arrays.asList("def123", "abc999", "zzz000", "abc123", "zzz111");

Comparator<String> cmp = new Comparator<String>() {
  public int compare(String o1, String o2) {
    int diff = (o1.substring(0,3)).compareTo(o2.substring(0,3));
        return (diff == 0) ? (Integer.valueOf(o2.substring(3)).compareTo(Integer.valueOf(o1.substring(3)))): diff;
  }
};
Collections.sort(list, cmp);

Answer 4

You should create a custom class including your String as an attribute. That class should implement the Comparable interface.

Inside your custom class you have to override method compareTo(T o) which was inherited from Comparable interface. You should apply your sorting logic there.

Then if you make a Collection (ex: List<CustomClass>) using that custom class as the object type, you can use Collections.sort(list) method to sort that List.

A complete example can be found here.

Answer 5

If you want more of an algorithmic approach, check this out: https://jsfiddle.net/5adpqgrc/1/

// start with ['def123', 'abc999', 'zzz000', 'abc123', 'zzz111']
var strings = ['def123', 'abc999', 'zzz000', 'abc123', 'zzz111']
$('body').append(strings.join(' ') + '<br>')

// reverse the digits
// get this ['def876', 'abc000', 'zzz999', 'abc876', 'zzz888']
strings = reverse_digits_only(strings)
$('body').append(strings.join(' ') + '<br>')

// sort it
// get this ['abc000', 'abc876', 'def876', 'zzz888', 'zzz999']
strings = strings.sort()
$('body').append(strings.join(' ') + '<br>')

// reverse the digits again
// get this ['abc999' 'abc123' 'def123' 'zzz111' 'zzz000']
strings = reverse_digits_only(strings)
$('body').append(strings.join(' ') + '<br>')


function reverse_digits_only (strings) {
    return strings.map(function (string) {
        var first_three_letters = string.substring(0, 3)
        var reversed_digits = string.substring(3).split('').map(function (digit) {
            return 9 - digit
        })

        return first_three_letters + reversed_digits.join('')
    })
}

How this works is that you:

1. Reverse the digits (abc999 becomes abc000)
2. Then sort it naturally
3. And then reverse the digits again.