public static <T extends Comparable<?>> List<T> topN(Iterable<T> coll, int n) {
		return Ordering.natural().greatestOf(coll, n);
	}
public static < T extends Comparable < ? > > List < T > topN ( Iterable < T > coll , int n ) { return Ordering . natural ( ) . greatestOf ( coll , n ) ; }
返回Iterable中最大的N个对象, back by guava.