Java Using Comparators in combination with custom Comparators

Question

I want to sort the following example list which currently contains only Strings with my own custom rules.

ArrayList<String> coll = new ArrayList<>();
coll.add("just");
coll.add("sdsd");
coll.add("asb");
coll.add("b as");
coll.add("just");
coll.add("dhfga");
coll.add("jusht");
coll.add("ktsa");
coll.add("just");
coll.add("just");

I know that I could write my own comparator for this, but as I know that Java also got comparators which solve this problem partially I want to know how I can use the ones from the Java API in combination with my own one.

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How should it be sorted?

The word just should always be the first word to appear in the list followed by all other words in alphabetical order.

Comparator.naturalOrder() sorts the list in alphabetical order, but how can I combine this comperator with a custom one which checks whether the word is just or something else.

Answer 1

You can do this something like that:

coll.sort(Comparator
    .comparingInt((String s) -> s.equals("just") ? 0 : 1) // Words "just" first
    .thenComparing(Comparator.naturalOrder())); // Then others

Answer 2

You could integrate the criteria into the comparator like

coll.sort(Comparator.comparing((String s) -> !s.equals("just"))
                    .thenComparing(Comparator.naturalOrder()));

or you separate the operations, first moving all occurrences of "just" to the front, then sorting the remaining elements only:

int howManyJust = 0;
for(int ix = 0, num = coll.size(); ix < num; ix++)
    if(coll.get(ix).equals("just") && ++howManyJust <= ix)
        Collections.swap(coll, ix, howManyJust-1);

coll.subList(howManyJust, coll.size()).sort(Comparator.naturalOrder());

while this may look more complicated, it is potentially more efficient, especially for larger lists.