java - Sort List<String> by priorised starting letters

Question

As an example, i have a list looking like this:

["a: foo", "b: bar", "c: foo", "d: bar"]

I want to sort it so a given priority, for example b > c > every other char. So the result should be:

["b: bar", "c: foo", "a: foo", "d: bar"]

Is there a simple way of doing this?

question from:https://stackoverflow.com/questions/66061727/sort-liststring-by-priorised-starting-letters

Answer 1

If you want the "B then C then other letters" sorting rule to apply to the entire string, not just the first letter, use a custom Collator.

Example

String addOnRule = "&b,B<c,C<a,A"; // Sort B then C before A
RuleBasedCollator standardCollator = (RuleBasedCollator) Collator.getInstance(Locale.US);
RuleBasedCollator customCollator = new RuleBasedCollator(standardCollator.getRules() + addOnRule);

String[] strings = { "a: foo", "b: bar", "c: foo", "d: bar", "aad", "aac", "aab", "aaa" };
Arrays.sort(strings, customCollator);
System.out.println(Arrays.toString(strings));

Output

[b: bar, c: foo, a: foo, aab, aac, aaa, aad, d: bar]