LeetCode Insert Interval

Given a set of non-overlapping intervals, insert a new interval into the intervals (merge if necessary).

You may assume that the intervals were initially sorted according to their start times.

Example 1:
Given intervals [1,3],[6,9], insert and merge [2,5] in as [1,5],[6,9].

Example 2:
Given [1,2],[3,5],[6,7],[8,10],[12,16], insert and merge [4,9] in as [1,2],[3,10],[12,16].

This is because the new interval [4,9] overlaps with [3,5],[6,7],[8,10].

 class intervalComparator implements Comparator<Interval>{
    @Override
    public int compare(Interval o1, Interval o2) {
        return o1.start-o2.start;
    }
}
public class Solution {
    public List<Interval> merge(List<Interval> intervals) {
        List<Interval> result = new ArrayList<Interval>();
        if (intervals.size() == 0) {
            return result;
        }
        Collections.sort(intervals, new intervalComparator());
        Interval first = intervals.get(0);
        Interval next;
        for (int i = 1; i <intervals.size() ; i++) {
            next = intervals.get(i);
            if (first.end < next.start) {
                result.add(first);
                first = next;
            } else {
                if (first.end < next.end) {
                    first.end = next.end;
                } 
            }
        }
        result.add(first);
        return result;
    }

    public List<Interval> insert(List<Interval> intervals, Interval newInterval) {
        List<Interval> result = new ArrayList<Interval>(intervals);
        result.add(newInterval);
        return merge(result);
    }
}