How to use Comparator in java with lambda expression?

Question

I am using lambda expression to sort 2D array based on multiple column but it failed while compiling.

public static void 2DarraySort(int[][] box) {
    Arrays.sort(box, Comparator.comparingInt(row -> row[0]).thenComparingInt(row -> row[1]));
}

Can someone please tell what wrong I am doing?

Error message:

array required, but java.lang.Object found

@0009laH what stack trace? They say it failed while *compiling*. — Federico klez Culloca, Aug 06 '21 at 08:11
See [comparing and thenComparing gives compile error](https://stackoverflow.com/questions/40500280/comparing-and-thencomparing-gives-compile-error) — , Aug 06 '21 at 08:35

score 0 · Answer 1 · answered Aug 06 '21 at 08:55

This would work fine if you have not chained the comparators:

Arrays.sort(box, Comparator.comparingInt(row -> row[0]));

However, when comparators are chained, the type of the objects being compared need to be specified explicitly, which may be done in two ways:

Arrays.sort(box, Comparator
    .<int[]>comparingInt(row -> row[0])
    .thenComparingInt(row -> row[1])
);

Arrays.sort(box, Comparator
    .comparingInt((int[] row ) -> row[0])
    .thenComparingInt(row -> row[1])
);

1 Answers1