What is the second argument doing in this function?

Question

Arrays.sort(courses, (a, b) -> a[1] - b[1]);
PriorityQueue<Integer> queue = new PriorityQueue<>((a, b) -> b - a);

I tried looking at the docs but cannot understand what the second argument is responsible for. I know that .sort(array, 1, 4) means sort from index 1 to 3. But in this case, the arrow with -> a[1] - b[1] and ((a, b) -> b - a) is what I am unable to understand.

Read about lambda notations in java. then it will make sense. — Kris, Jun 23 '22 at 06:41
You can review this - https://stackoverflow.com/a/21970805/7357959 — Tsvetoslav Tsvetkov, Jun 23 '22 at 06:42
@AddeusExMachina "courses" is the actual list that has to be sorted — Tsvetoslav Tsvetkov, Jun 23 '22 at 06:43
@sdfesvrtae4t4fw4efawef, you should try to understand the parameters of sort function in java, lambda notations.Then it will be very clear — Kris, Jun 23 '22 at 06:44

score 0 · Accepted Answer · answered Jun 23 '22 at 06:43

The arrow represents a lambda function that compares any two arguments a and b. Before lambdas were introduced (in Java 8), the sort would look like this:

Arrays.sort(courses, new Comparator<int[]>() {
    @Override
    public int compare(int[] a, int[] b) {
        return a[1] - b[1];
    }
});

I'm taking a guess at the type of a but feel free to substitute int[] with any numeric array.

What is the second argument doing in this function?

1 Answers1