Tada

Map<Integer, Integer> map = new HashMap<>();
map.put(0, -1);

is same as:

//Map<Integer, Integer> map = new HashMap<>();;

How?

It is actually called double brace initalisation which is discussed in https://leetcode.com/problems/continuous-subarray-sum/solutions/99499/java-o-n-time-o-k-space/?orderBy=most_votes comments