ICU-13620 Adding comment.

X-SVN-Rev: 41057

diff --git a/icu4j/main/classes/core/src/com/ibm/icu/util/MeasureUnit.java b/icu4j/main/classes/core/src/com/ibm/icu/util/MeasureUnit.java
index d35c8dd8c0d4db494fda31c6c5aa0ac5dc247fff..95b6c3e27d04986508a5210bb62193493793fd51 100644 (file)
--- a/icu4j/main/classes/core/src/com/ibm/icu/util/MeasureUnit.java
+++ b/icu4j/main/classes/core/src/com/ibm/icu/util/MeasureUnit.java
@@ -150,6 +150,7 @@ public class MeasureUnit implements Serializable {
         Map<String, MeasureUnit> units = cache.get(type);
         // Train users not to modify returned set from the start giving us more
         // flexibility for implementation.
+        // Use CollectionSet instead of HashSet for better performance.
         return units == null ? Collections.<MeasureUnit>emptySet()
                 : Collections.unmodifiableSet(new CollectionSet<MeasureUnit>(units.values()));
     }