diff --git a/base/src/main/java/smile/graph/NearestNeighborGraph.java b/base/src/main/java/smile/graph/NearestNeighborGraph.java
index 8a6987366..03da54dc5 100644
--- a/base/src/main/java/smile/graph/NearestNeighborGraph.java
+++ b/base/src/main/java/smile/graph/NearestNeighborGraph.java
@@ -438,7 +438,7 @@ private static int[][] generateCandidates(List<PriorityQueue<Neighbor>> heapList
         int[][] result = new int[n][];
         for (int i = 0; i < n; i++) {
             List<Neighbor> list = new ArrayList<>(candidates.get(i));
-            list.sort((o1, o2) -> Double.compare(o1.distance, o2.distance));
+            list.sort(Comparator.comparingDouble(o -> o.distance));
             result[i] = list.stream().limit(maxCandidates).mapToInt(neighbor -> neighbor.index).toArray();
         }
         return result;