RFR 8020156/8020009 TreeMap.values should report ORDERED/TreeMap.entrySet comparator should not be null

[Paul Sandoz]

Hi,

Please review the following patch that fixes two issues with TreeMap spliterators:

  http://cr.openjdk.java.net/~psandoz/tl/JDK-8020156-8020009-TreeMap/webrev/

It's unfortunate and damn ugly that i resorted to using raw types and a cast for the EntrySet Spliterator.getComparator method: 

+            // Since SORTED is reported and Map.Entry elements are not comparable
+            // then a non-null comparator needs to be returned
+            if (tree.comparator != null) {
+                // Adapt the existing non-null comparator to compare entries
+                // by key
+                return Map.Entry.comparingByKey(tree.comparator);
+            }
+            else {
+                // Return a comparator of entries by key, with K assumed to be
+                // of Comparable
+                // First obtain the Map.Entry.comparingByKey() comparator
+                // as a raw type since K is not declared with
+                // a upper bound of Comparable, then cast to the return type
+                @SuppressWarnings("rawtypes")
+                Comparator craw = Map.Entry.comparingByKey();
+                @SuppressWarnings("unchecked")
+                Comparator<? super Map.Entry<K, V>> c =
+                        (Comparator<? super Map.Entry<K, V>>) craw;
+                return c;
+            }


Perhaps rather than reusing a Map.Entry comparator method it is clearer to do the following:

                return (Comparator<? super Map.Entry<K, V>> & Serializable) (e1, e2) -> {
                    @SuppressWarnings("unchecked")
                    Comparable<? super K> k1 = (Comparable<? super K>) e1.getKey();
                    return k1.compareTo(e2.getKey());
                };

? I marginally prefer that.

I created a new test java/util/Spliterators/SpliteratorCharacteristics that we can fill out over time for other collections as and when needed.

Paul.