[GitHub] [hadoop] goiri commented on a change in pull request #1974: HADOOP-17009: Embrace Immutability of Java Collections

[GitBox]

goiri commented on a change in pull request #1974:
URL: https://github.com/apache/hadoop/pull/1974#discussion_r415103835



##
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/NetworkTopology.java
##
@@ -196,10 +196,8 @@ protected Node getNodeForNetworkLocation(Node node) {
 loc = loc.substring(1);
   }
   InnerNode rack = (InnerNode) clusterMap.getLoc(loc);
-  if (rack == null) {
-return null;
-  }
-  return new ArrayList(rack.getChildren());
+  return (rack == null) ? Collections.emptyList()

Review comment:
   Why can we use unmodifiable here?





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[GitHub] [hadoop] goiri commented on a change in pull request #1974: HADOOP-17009: Embrace Immutability of Java Collections

[GitBox]

goiri commented on a change in pull request #1974:
URL: https://github.com/apache/hadoop/pull/1974#discussion_r414009203



##
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/CompositeGroupsMapping.java
##
@@ -78,15 +79,13 @@
 user, provider.getClass().getSimpleName(), e.toString());
 LOG.debug("Stacktrace: ", e);
   }
-  if (groups != null && ! groups.isEmpty()) {
+  if (!groups.isEmpty()) {
 groupSet.addAll(groups);
 if (!combined) break;
   }
 }
 
-List results = new ArrayList(groupSet.size());
-results.addAll(groupSet);
-return results;
+return Collections.unmodifiableList(new ArrayList<>(groupSet));

Review comment:
   Now, somebody calling getGroups() would start failing if it was adding 
new things to the list while that was not the case before. I've tried using 
inmodifiable before but is kind of dangerous.





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