Add Checker Framework annotations in comments (issue #359).

Putting the annotations in comments allows us to use Java 8 syntax and avoid
depending on the Checker Framework library.  Note that we need to use
org.checkerframework.checker.nullness.qual.Nullable for marking types nullable,
because javax.annotation.Nullable can't be applied to types.

3 files changed, 34 insertions, 20 deletions

diff --git a/impl_core/src/main/java/io/opencensus/implcore/stats/IntervalBucket.java b/impl_core/src/main/java/io/opencensus/implcore/stats/IntervalBucket.java
index 68380791..a35948a7 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/stats/IntervalBucket.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/stats/IntervalBucket.java
@@ -28,6 +28,10 @@ import io.opencensus.tags.TagValue;
 import java.util.List;
 import java.util.Map;
 
+/*>>>
+import org.checkerframework.checker.nullness.qual.Nullable;
+*/
+
 /** The bucket with aggregated {@code MeasureValue}s used for {@code IntervalViewData}. */
 final class IntervalBucket {
 
@@ -36,7 +40,8 @@ final class IntervalBucket {
   private final Timestamp start;
   private final Duration duration;
   private final Aggregation aggregation;
-  private final Map<List<TagValue>, MutableAggregation> tagValueAggregationMap = Maps.newHashMap();
+  private final Map<List</*@Nullable*/ TagValue>, MutableAggregation> tagValueAggregationMap =
+      Maps.newHashMap();
 
   IntervalBucket(Timestamp start, Duration duration, Aggregation aggregation) {
     checkNotNull(start, "Start");
@@ -48,7 +53,7 @@ final class IntervalBucket {
     this.aggregation = aggregation;
   }
 
-  Map<List<TagValue>, MutableAggregation> getTagValueAggregationMap() {
+  Map<List</*@Nullable*/ TagValue>, MutableAggregation> getTagValueAggregationMap() {
     return tagValueAggregationMap;
   }
 
@@ -57,7 +62,7 @@ final class IntervalBucket {
   }
 
   // Puts a new value into the internal MutableAggregations, based on the TagValues.
-  void record(List<TagValue> tagValues, double value) {
+  void record(List</*@Nullable*/ TagValue> tagValues, double value) {
     if (!tagValueAggregationMap.containsKey(tagValues)) {
       tagValueAggregationMap.put(tagValues, MutableViewData.createMutableAggregation(aggregation));
     }
diff --git a/impl_core/src/main/java/io/opencensus/implcore/stats/MeasureToViewMap.java b/impl_core/src/main/java/io/opencensus/implcore/stats/MeasureToViewMap.java
index 4e55c741..64173713 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/stats/MeasureToViewMap.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/stats/MeasureToViewMap.java
@@ -40,9 +40,12 @@ import java.util.Iterator;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
-import javax.annotation.Nullable;
 import javax.annotation.concurrent.GuardedBy;
 
+/*>>>
+import org.checkerframework.checker.nullness.qual.Nullable;
+*/
+
 /** A class that stores a singleton map from {@code MeasureName}s to {@link MutableViewData}s. */
 final class MeasureToViewMap {
 
@@ -63,10 +66,10 @@ final class MeasureToViewMap {
 
   // Cached set of exported views. It must be set to null whenever a view is registered or
   // unregistered.
-  @Nullable private volatile Set<View> exportedViews;
+  @javax.annotation.Nullable private volatile Set<View> exportedViews;
 
   /** Returns a {@link ViewData} corresponding to the given {@link View.Name}. */
-  @Nullable
+  @javax.annotation.Nullable
   synchronized ViewData getView(View.Name viewName, Clock clock, StatsCollectionState state) {
     MutableViewData view = getMutableViewData(viewName);
     return view == null ? null : view.toViewData(clock.now(), state);
@@ -119,7 +122,7 @@ final class MeasureToViewMap {
     mutableMap.put(view.getMeasure().getName(), MutableViewData.create(view, clock.now()));
   }
 
-  @Nullable
+  @javax.annotation.Nullable
   private synchronized MutableViewData getMutableViewData(View.Name viewName) {
     View view = registeredViews.get(viewName);
     if (view == null) {
@@ -155,7 +158,7 @@ final class MeasureToViewMap {
         measurement.match(
             new RecordDoubleValueFunc(tags, view, timestamp),
             new RecordLongValueFunc(tags, view, timestamp),
-            Functions.<Void>throwAssertionError());
+            Functions.</*@Nullable*/ Void>throwAssertionError());
       }
     }
   }
diff --git a/impl_core/src/main/java/io/opencensus/implcore/stats/MutableViewData.java b/impl_core/src/main/java/io/opencensus/implcore/stats/MutableViewData.java
index 7d251559..4963ce59 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/stats/MutableViewData.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/stats/MutableViewData.java
@@ -63,7 +63,10 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
-import javax.annotation.Nullable;
+
+/*>>>
+import org.checkerframework.checker.nullness.qual.Nullable;
+*/
 
 /** A mutable version of {@link ViewData}, used for recording stats and start/end time. */
 abstract class MutableViewData {
@@ -71,7 +74,7 @@ abstract class MutableViewData {
   private static final long MILLIS_PER_SECOND = 1000L;
   private static final long NANOS_PER_MILLI = 1000 * 1000;
 
-  @Nullable @VisibleForTesting static final TagValue UNKNOWN_TAG_VALUE = null;
+  @javax.annotation.Nullable @VisibleForTesting static final TagValue UNKNOWN_TAG_VALUE = null;
 
   @VisibleForTesting static final Timestamp ZERO_TIMESTAMP = Timestamp.create(0, 0);
 
@@ -134,9 +137,9 @@ abstract class MutableViewData {
   }
 
   @VisibleForTesting
-  static List<TagValue> getTagValues(
+  static List</*@Nullable*/ TagValue> getTagValues(
       Map<? extends TagKey, ? extends TagValue> tags, List<? extends TagKey> columns) {
-    List<TagValue> tagValues = new ArrayList<TagValue>(columns.size());
+    List</*@Nullable*/ TagValue> tagValues = new ArrayList</*@Nullable*/ TagValue>(columns.size());
     // Record all the measures in a "Greedy" way.
     // Every view aggregates every measure. This is similar to doing a GROUPBY view’s keys.
     for (int i = 0; i < columns.size(); ++i) {
@@ -202,7 +205,7 @@ abstract class MutableViewData {
   private static final class CumulativeMutableViewData extends MutableViewData {
 
     private Timestamp start;
-    private final Map<List<TagValue>, MutableAggregation> tagValueAggregationMap =
+    private final Map<List</*@Nullable*/ TagValue>, MutableAggregation> tagValueAggregationMap =
         Maps.newHashMap();
 
     private CumulativeMutableViewData(View view, Timestamp start) {
@@ -212,7 +215,8 @@ abstract class MutableViewData {
 
     @Override
     void record(TagContext context, double value, Timestamp timestamp) {
-      List<TagValue> tagValues = getTagValues(getTagMap(context), super.view.getColumns());
+      List</*@Nullable*/ TagValue> tagValues =
+          getTagValues(getTagMap(context), super.view.getColumns());
       if (!tagValueAggregationMap.containsKey(tagValues)) {
         tagValueAggregationMap.put(
             tagValues, createMutableAggregation(super.view.getAggregation()));
@@ -305,7 +309,8 @@ abstract class MutableViewData {
 
     @Override
     void record(TagContext context, double value, Timestamp timestamp) {
-      List<TagValue> tagValues = getTagValues(getTagMap(context), super.view.getColumns());
+      List</*@Nullable*/ TagValue> tagValues =
+          getTagValues(getTagMap(context), super.view.getColumns());
       refreshBucketList(timestamp);
       // It is always the last bucket that does the recording.
       NullnessUtils.castNonNull(buckets.peekLast()).record(tagValues, value);
@@ -390,8 +395,9 @@ abstract class MutableViewData {
 
     // Combine stats within each bucket, aggregate stats by tag values, and return the mapping from
     // tag values to aggregation data.
-    private Map<List<TagValue>, AggregationData> combineBucketsAndGetAggregationMap(Timestamp now) {
-      Multimap<List<TagValue>, MutableAggregation> multimap = HashMultimap.create();
+    private Map<List</*@Nullable*/ TagValue>, AggregationData> combineBucketsAndGetAggregationMap(
+        Timestamp now) {
+      Multimap<List</*@Nullable*/ TagValue>, MutableAggregation> multimap = HashMultimap.create();
 
       // TODO(sebright): Decide whether to use a different class instead of LinkedList.
       @SuppressWarnings("JdkObsolete")
@@ -399,7 +405,7 @@ abstract class MutableViewData {
 
       Aggregation aggregation = super.view.getAggregation();
       putBucketsIntoMultiMap(shallowCopy, multimap, aggregation, now);
-      Map<List<TagValue>, MutableAggregation> singleMap =
+      Map<List</*@Nullable*/ TagValue>, MutableAggregation> singleMap =
           aggregateOnEachTagValueList(multimap, aggregation);
       return createAggregationMap(singleMap, super.getView().getMeasure());
     }
@@ -408,7 +414,7 @@ abstract class MutableViewData {
     // mutable aggregations (map value) from different buckets.
     private static void putBucketsIntoMultiMap(
         LinkedList<IntervalBucket> buckets,
-        Multimap<List<TagValue>, MutableAggregation> multimap,
+        Multimap<List</*@Nullable*/ TagValue>, MutableAggregation> multimap,
         Aggregation aggregation,
         Timestamp now) {
       // Put fractional stats of the head (oldest) bucket.
@@ -430,7 +436,7 @@ abstract class MutableViewData {
           shouldSkipFirst = false;
           continue; // skip the first bucket
         }
-        for (Entry<List<TagValue>, MutableAggregation> entry :
+        for (Entry<List</*@Nullable*/ TagValue>, MutableAggregation> entry :
             bucket.getTagValueAggregationMap().entrySet()) {
           multimap.put(entry.getKey(), entry.getValue());
         }