usage of comparator in Java

1

int[][] nums = new int[][]{{1,2,3},{4,5,6}}; 
Arrays.sort(nums, (a,b)->(a[0]-b[0]));

Queue<Integer> maxHeap = new PriorityQueue<>((a1, a2) -> (a2 - a1));

2

Map<int[], Integer> map = new TreeMap<>(new Comparator<int[]>() {
            @Override
            public int compare(int[] o1, int[] o2) {
                if (o1[1] < o2[1]) {
                    return -1;
                }
                return 1;
            }
        });