LeetCode Merge Intervals

Given a collection of intervals, merge all overlapping intervals.

For example,
Given [1,3],[2,6],[8,10],[15,18],
return [1,6],[8,10],[15,18].

/**
 * Definition for an interval.
 * public class Interval {
 *     int start;
 *     int end;
 *     Interval() { start = 0; end = 0; }
 *     Interval(int s, int e) { start = s; end = e; }
 * }
 */
 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;
    }
}