```
public int maxSubArrayLen(int[] nums, int k) {
int sum = 0, max = 0;
HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
for (int i = 0; i < nums.length; i++) {
sum = sum + nums[i];
if (sum == k) max = i + 1;
else if (map.containsKey(sum - k)) max = Math.max(max, i - map.get(sum - k));
if (!map.containsKey(sum)) map.put(sum, i);
}
return max;
}
```

The HashMap stores the sum of all elements before index i as key, and i as value. For each i, check not only the current sum but also (currentSum - previousSum) to see if there is any that equals k, and update max length.

PS: An "else" is added. Thanks to beckychiu1988 for comment.