Cleanup: Move static util methods to util class. (#1343)

* Cleanup: Move static util methods to util class.

* Fix checker framework.

9 files changed, 480 insertions, 436 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 12cb319e..75efabf7 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
@@ -67,7 +67,7 @@ final class IntervalBucket {
       Map<String, String> attachments,
       Timestamp timestamp) {
     if (!tagValueAggregationMap.containsKey(tagValues)) {
-      tagValueAggregationMap.put(tagValues, MutableViewData.createMutableAggregation(aggregation));
+      tagValueAggregationMap.put(tagValues, RecordUtils.createMutableAggregation(aggregation));
     }
     tagValueAggregationMap.get(tagValues).add(value, attachments, timestamp);
   }
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 b5917289..79e913db 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
@@ -21,13 +21,9 @@ import com.google.common.collect.Maps;
 import com.google.common.collect.Multimap;
 import com.google.common.collect.Sets;
 import io.opencensus.common.Clock;
-import io.opencensus.common.Function;
-import io.opencensus.common.Functions;
 import io.opencensus.common.Timestamp;
 import io.opencensus.stats.Measure;
 import io.opencensus.stats.Measurement;
-import io.opencensus.stats.Measurement.MeasurementDouble;
-import io.opencensus.stats.Measurement.MeasurementLong;
 import io.opencensus.stats.StatsCollectionState;
 import io.opencensus.stats.View;
 import io.opencensus.stats.ViewData;
@@ -156,10 +152,8 @@ final class MeasureToViewMap {
       }
       Collection<MutableViewData> views = mutableMap.get(measure.getName());
       for (MutableViewData view : views) {
-        measurement.match(
-            new RecordDoubleValueFunc(tags, view, timestamp, attachments),
-            new RecordLongValueFunc(tags, view, timestamp, attachments),
-            Functions.</*@Nullable*/ Void>throwAssertionError());
+        view.record(
+            tags, RecordUtils.getDoubleValueFromMeasurement(measurement), timestamp, attachments);
       }
     }
   }
@@ -181,52 +175,4 @@ final class MeasureToViewMap {
       }
     }
   }
-
-  private static final class RecordDoubleValueFunc implements Function<MeasurementDouble, Void> {
-    @Override
-    public Void apply(MeasurementDouble arg) {
-      view.record(tags, arg.getValue(), timestamp, attachments);
-      return null;
-    }
-
-    private final TagContext tags;
-    private final MutableViewData view;
-    private final Timestamp timestamp;
-    private final Map<String, String> attachments;
-
-    private RecordDoubleValueFunc(
-        TagContext tags,
-        MutableViewData view,
-        Timestamp timestamp,
-        Map<String, String> attachments) {
-      this.tags = tags;
-      this.view = view;
-      this.timestamp = timestamp;
-      this.attachments = attachments;
-    }
-  }
-
-  private static final class RecordLongValueFunc implements Function<MeasurementLong, Void> {
-    @Override
-    public Void apply(MeasurementLong arg) {
-      view.record(tags, arg.getValue(), timestamp, attachments);
-      return null;
-    }
-
-    private final TagContext tags;
-    private final MutableViewData view;
-    private final Timestamp timestamp;
-    private final Map<String, String> attachments;
-
-    private RecordLongValueFunc(
-        TagContext tags,
-        MutableViewData view,
-        Timestamp timestamp,
-        Map<String, String> attachments) {
-      this.tags = tags;
-      this.view = view;
-      this.timestamp = timestamp;
-      this.attachments = attachments;
-    }
-  }
 }
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 df99ecfb..876415a3 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
@@ -17,6 +17,10 @@
 package io.opencensus.implcore.stats;
 
 import static com.google.common.base.Preconditions.checkArgument;
+import static io.opencensus.implcore.stats.RecordUtils.createAggregationMap;
+import static io.opencensus.implcore.stats.RecordUtils.createMutableAggregation;
+import static io.opencensus.implcore.stats.RecordUtils.getTagMap;
+import static io.opencensus.implcore.stats.RecordUtils.getTagValues;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.LinkedHashMultimap;
@@ -27,37 +31,14 @@ import io.opencensus.common.Function;
 import io.opencensus.common.Functions;
 import io.opencensus.common.Timestamp;
 import io.opencensus.implcore.internal.CheckerFrameworkUtils;
-import io.opencensus.implcore.stats.MutableAggregation.MutableCount;
-import io.opencensus.implcore.stats.MutableAggregation.MutableDistribution;
-import io.opencensus.implcore.stats.MutableAggregation.MutableLastValue;
-import io.opencensus.implcore.stats.MutableAggregation.MutableMean;
-import io.opencensus.implcore.stats.MutableAggregation.MutableSum;
-import io.opencensus.implcore.tags.TagContextImpl;
 import io.opencensus.stats.Aggregation;
-import io.opencensus.stats.Aggregation.Count;
-import io.opencensus.stats.Aggregation.Distribution;
-import io.opencensus.stats.Aggregation.LastValue;
-import io.opencensus.stats.Aggregation.Sum;
 import io.opencensus.stats.AggregationData;
-import io.opencensus.stats.AggregationData.CountData;
-import io.opencensus.stats.AggregationData.DistributionData;
-import io.opencensus.stats.AggregationData.DistributionData.Exemplar;
-import io.opencensus.stats.AggregationData.LastValueDataDouble;
-import io.opencensus.stats.AggregationData.LastValueDataLong;
-import io.opencensus.stats.AggregationData.SumDataDouble;
-import io.opencensus.stats.AggregationData.SumDataLong;
-import io.opencensus.stats.Measure;
 import io.opencensus.stats.StatsCollectionState;
 import io.opencensus.stats.View;
 import io.opencensus.stats.ViewData;
-import io.opencensus.tags.InternalUtils;
-import io.opencensus.tags.Tag;
 import io.opencensus.tags.TagContext;
-import io.opencensus.tags.TagKey;
 import io.opencensus.tags.TagValue;
-import java.util.ArrayList;
 import java.util.Collections;
-import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -71,8 +52,6 @@ import org.checkerframework.checker.nullness.qual.Nullable;
 @SuppressWarnings("deprecation")
 abstract class MutableViewData {
 
-  @javax.annotation.Nullable @VisibleForTesting static final TagValue UNKNOWN_TAG_VALUE = null;
-
   @VisibleForTesting static final Timestamp ZERO_TIMESTAMP = Timestamp.create(0, 0);
 
   private final View view;
@@ -101,16 +80,10 @@ abstract class MutableViewData {
     return view;
   }
 
-  /** Record double stats with the given tags. */
+  /** Record stats with the given tags. */
   abstract void record(
       TagContext context, double value, Timestamp timestamp, Map<String, String> attachments);
 
-  /** Record long stats with the given tags. */
-  void record(TagContext tags, long value, Timestamp timestamp, Map<String, String> attachments) {
-    // TODO(songya): shall we check for precision loss here?
-    record(tags, (double) value, timestamp, attachments);
-  }
-
   /** Convert this {@link MutableViewData} to {@link ViewData}. */
   abstract ViewData toViewData(Timestamp now, StatsCollectionState state);
 
@@ -121,81 +94,6 @@ abstract class MutableViewData {
   // bucket list (for InternalMutableViewData).
   abstract void resumeStatsCollection(Timestamp now);
 
-  private static Map<TagKey, TagValue> getTagMap(TagContext ctx) {
-    if (ctx instanceof TagContextImpl) {
-      return ((TagContextImpl) ctx).getTags();
-    } else {
-      Map<TagKey, TagValue> tags = Maps.newHashMap();
-      for (Iterator<Tag> i = InternalUtils.getTags(ctx); i.hasNext(); ) {
-        Tag tag = i.next();
-        tags.put(tag.getKey(), tag.getValue());
-      }
-      return tags;
-    }
-  }
-
-  @VisibleForTesting
-  static List</*@Nullable*/ TagValue> getTagValues(
-      Map<? extends TagKey, ? extends TagValue> tags, List<? extends TagKey> columns) {
-    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) {
-      TagKey tagKey = columns.get(i);
-      if (!tags.containsKey(tagKey)) {
-        // replace not found key values by null.
-        tagValues.add(UNKNOWN_TAG_VALUE);
-      } else {
-        tagValues.add(tags.get(tagKey));
-      }
-    }
-    return tagValues;
-  }
-
-  /**
-   * Create an empty {@link MutableAggregation} based on the given {@link Aggregation}.
-   *
-   * @param aggregation {@code Aggregation}.
-   * @return an empty {@code MutableAggregation}.
-   */
-  @VisibleForTesting
-  static MutableAggregation createMutableAggregation(Aggregation aggregation) {
-    return aggregation.match(
-        CreateMutableSum.INSTANCE,
-        CreateMutableCount.INSTANCE,
-        CreateMutableDistribution.INSTANCE,
-        CreateMutableLastValue.INSTANCE,
-        AggregationDefaultFunction.INSTANCE);
-  }
-
-  /**
-   * Create an {@link AggregationData} snapshot based on the given {@link MutableAggregation}.
-   *
-   * @param aggregation {@code MutableAggregation}
-   * @param measure {@code Measure}
-   * @return an {@code AggregationData} which is the snapshot of current summary statistics.
-   */
-  @VisibleForTesting
-  static AggregationData createAggregationData(MutableAggregation aggregation, Measure measure) {
-    return aggregation.match(
-        new CreateSumData(measure),
-        CreateCountData.INSTANCE,
-        CreateMeanData.INSTANCE,
-        CreateDistributionData.INSTANCE,
-        new CreateLastValueData(measure));
-  }
-
-  // Covert a mapping from TagValues to MutableAggregation, to a mapping from TagValues to
-  // AggregationData.
-  private static <T> Map<T, AggregationData> createAggregationMap(
-      Map<T, MutableAggregation> tagValueAggregationMap, Measure measure) {
-    Map<T, AggregationData> map = Maps.newHashMap();
-    for (Entry<T, MutableAggregation> entry : tagValueAggregationMap.entrySet()) {
-      map.put(entry.getKey(), createAggregationData(entry.getValue(), measure));
-    }
-    return map;
-  }
-
   private static final class CumulativeMutableViewData extends MutableViewData {
 
     private Timestamp start;
@@ -483,145 +381,6 @@ abstract class MutableViewData {
     }
   }
 
-  // static inner Function classes
-
-  private static final class CreateMutableSum implements Function<Sum, MutableAggregation> {
-    @Override
-    public MutableAggregation apply(Sum arg) {
-      return MutableSum.create();
-    }
-
-    private static final CreateMutableSum INSTANCE = new CreateMutableSum();
-  }
-
-  private static final class CreateMutableCount implements Function<Count, MutableAggregation> {
-    @Override
-    public MutableAggregation apply(Count arg) {
-      return MutableCount.create();
-    }
-
-    private static final CreateMutableCount INSTANCE = new CreateMutableCount();
-  }
-
-  // TODO(songya): remove this once Mean aggregation is completely removed. Before that
-  // we need to continue supporting Mean, since it could still be used by users and some
-  // deprecated RPC views.
-  private static final class AggregationDefaultFunction
-      implements Function<Aggregation, MutableAggregation> {
-    @Override
-    public MutableAggregation apply(Aggregation arg) {
-      if (arg instanceof Aggregation.Mean) {
-        return MutableMean.create();
-      }
-      throw new IllegalArgumentException("Unknown Aggregation.");
-    }
-
-    private static final AggregationDefaultFunction INSTANCE = new AggregationDefaultFunction();
-  }
-
-  private static final class CreateMutableDistribution
-      implements Function<Distribution, MutableAggregation> {
-    @Override
-    public MutableAggregation apply(Distribution arg) {
-      return MutableDistribution.create(arg.getBucketBoundaries());
-    }
-
-    private static final CreateMutableDistribution INSTANCE = new CreateMutableDistribution();
-  }
-
-  private static final class CreateMutableLastValue
-      implements Function<LastValue, MutableAggregation> {
-    @Override
-    public MutableAggregation apply(LastValue arg) {
-      return MutableLastValue.create();
-    }
-
-    private static final CreateMutableLastValue INSTANCE = new CreateMutableLastValue();
-  }
-
-  private static final class CreateSumData implements Function<MutableSum, AggregationData> {
-
-    private final Measure measure;
-
-    private CreateSumData(Measure measure) {
-      this.measure = measure;
-    }
-
-    @Override
-    public AggregationData apply(final MutableSum arg) {
-      return measure.match(
-          Functions.<AggregationData>returnConstant(SumDataDouble.create(arg.getSum())),
-          Functions.<AggregationData>returnConstant(SumDataLong.create(Math.round(arg.getSum()))),
-          Functions.<AggregationData>throwAssertionError());
-    }
-  }
-
-  private static final class CreateCountData implements Function<MutableCount, AggregationData> {
-    @Override
-    public AggregationData apply(MutableCount arg) {
-      return CountData.create(arg.getCount());
-    }
-
-    private static final CreateCountData INSTANCE = new CreateCountData();
-  }
-
-  private static final class CreateMeanData implements Function<MutableMean, AggregationData> {
-    @Override
-    public AggregationData apply(MutableMean arg) {
-      return AggregationData.MeanData.create(arg.getMean(), arg.getCount());
-    }
-
-    private static final CreateMeanData INSTANCE = new CreateMeanData();
-  }
-
-  private static final class CreateDistributionData
-      implements Function<MutableDistribution, AggregationData> {
-    @Override
-    public AggregationData apply(MutableDistribution arg) {
-      List<Long> boxedBucketCounts = new ArrayList<Long>();
-      for (long bucketCount : arg.getBucketCounts()) {
-        boxedBucketCounts.add(bucketCount);
-      }
-      List<Exemplar> exemplars = new ArrayList<Exemplar>();
-      if (arg.getExemplars() != null) {
-        for (Exemplar exemplar : arg.getExemplars()) {
-          if (exemplar != null) {
-            exemplars.add(exemplar);
-          }
-        }
-      }
-      return DistributionData.create(
-          arg.getMean(),
-          arg.getCount(),
-          arg.getMin(),
-          arg.getMax(),
-          arg.getSumOfSquaredDeviations(),
-          boxedBucketCounts,
-          exemplars);
-    }
-
-    private static final CreateDistributionData INSTANCE = new CreateDistributionData();
-  }
-
-  private static final class CreateLastValueData
-      implements Function<MutableLastValue, AggregationData> {
-
-    private final Measure measure;
-
-    private CreateLastValueData(Measure measure) {
-      this.measure = measure;
-    }
-
-    @Override
-    public AggregationData apply(final MutableLastValue arg) {
-      return measure.match(
-          Functions.<AggregationData>returnConstant(LastValueDataDouble.create(arg.getLastValue())),
-          Functions.<AggregationData>returnConstant(
-              LastValueDataLong.create(Math.round(arg.getLastValue()))),
-          Functions.<AggregationData>throwAssertionError());
-    }
-  }
-
   private static final class CreateCumulative
       implements Function<View.AggregationWindow.Cumulative, MutableViewData> {
     @Override
diff --git a/impl_core/src/main/java/io/opencensus/implcore/stats/RecordUtils.java b/impl_core/src/main/java/io/opencensus/implcore/stats/RecordUtils.java
new file mode 100644
index 00000000..5dc77cb1
--- /dev/null
+++ b/impl_core/src/main/java/io/opencensus/implcore/stats/RecordUtils.java
@@ -0,0 +1,306 @@
+/*
+ * Copyright 2018, OpenCensus Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.opencensus.implcore.stats;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.Maps;
+import io.opencensus.common.Function;
+import io.opencensus.common.Functions;
+import io.opencensus.implcore.stats.MutableAggregation.MutableCount;
+import io.opencensus.implcore.stats.MutableAggregation.MutableDistribution;
+import io.opencensus.implcore.stats.MutableAggregation.MutableLastValue;
+import io.opencensus.implcore.stats.MutableAggregation.MutableMean;
+import io.opencensus.implcore.stats.MutableAggregation.MutableSum;
+import io.opencensus.implcore.tags.TagContextImpl;
+import io.opencensus.stats.Aggregation;
+import io.opencensus.stats.Aggregation.Count;
+import io.opencensus.stats.Aggregation.Distribution;
+import io.opencensus.stats.Aggregation.LastValue;
+import io.opencensus.stats.Aggregation.Sum;
+import io.opencensus.stats.AggregationData;
+import io.opencensus.stats.AggregationData.CountData;
+import io.opencensus.stats.AggregationData.DistributionData;
+import io.opencensus.stats.AggregationData.DistributionData.Exemplar;
+import io.opencensus.stats.AggregationData.LastValueDataDouble;
+import io.opencensus.stats.AggregationData.LastValueDataLong;
+import io.opencensus.stats.AggregationData.SumDataDouble;
+import io.opencensus.stats.AggregationData.SumDataLong;
+import io.opencensus.stats.Measure;
+import io.opencensus.stats.Measurement;
+import io.opencensus.stats.Measurement.MeasurementDouble;
+import io.opencensus.stats.Measurement.MeasurementLong;
+import io.opencensus.tags.InternalUtils;
+import io.opencensus.tags.Tag;
+import io.opencensus.tags.TagContext;
+import io.opencensus.tags.TagKey;
+import io.opencensus.tags.TagValue;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+
+/*>>>
+import org.checkerframework.checker.nullness.qual.Nullable;
+*/
+
+@SuppressWarnings("deprecation")
+/* Common static utilities for stats recording. */
+final class RecordUtils {
+
+  @javax.annotation.Nullable @VisibleForTesting static final TagValue UNKNOWN_TAG_VALUE = null;
+
+  static Map<TagKey, TagValue> getTagMap(TagContext ctx) {
+    if (ctx instanceof TagContextImpl) {
+      return ((TagContextImpl) ctx).getTags();
+    } else {
+      Map<TagKey, TagValue> tags = Maps.newHashMap();
+      for (Iterator<Tag> i = InternalUtils.getTags(ctx); i.hasNext(); ) {
+        Tag tag = i.next();
+        tags.put(tag.getKey(), tag.getValue());
+      }
+      return tags;
+    }
+  }
+
+  @VisibleForTesting
+  static List</*@Nullable*/ TagValue> getTagValues(
+      Map<? extends TagKey, ? extends TagValue> tags, List<? extends TagKey> columns) {
+    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) {
+      TagKey tagKey = columns.get(i);
+      if (!tags.containsKey(tagKey)) {
+        // replace not found key values by null.
+        tagValues.add(UNKNOWN_TAG_VALUE);
+      } else {
+        tagValues.add(tags.get(tagKey));
+      }
+    }
+    return tagValues;
+  }
+
+  /**
+   * Create an empty {@link MutableAggregation} based on the given {@link Aggregation}.
+   *
+   * @param aggregation {@code Aggregation}.
+   * @return an empty {@code MutableAggregation}.
+   */
+  @VisibleForTesting
+  static MutableAggregation createMutableAggregation(Aggregation aggregation) {
+    return aggregation.match(
+        CreateMutableSum.INSTANCE,
+        CreateMutableCount.INSTANCE,
+        CreateMutableDistribution.INSTANCE,
+        CreateMutableLastValue.INSTANCE,
+        AggregationDefaultFunction.INSTANCE);
+  }
+
+  /**
+   * Create an {@link AggregationData} snapshot based on the given {@link MutableAggregation}.
+   *
+   * @param aggregation {@code MutableAggregation}
+   * @param measure {@code Measure}
+   * @return an {@code AggregationData} which is the snapshot of current summary statistics.
+   */
+  @VisibleForTesting
+  static AggregationData createAggregationData(MutableAggregation aggregation, Measure measure) {
+    return aggregation.match(
+        new CreateSumData(measure),
+        CreateCountData.INSTANCE,
+        CreateMeanData.INSTANCE,
+        CreateDistributionData.INSTANCE,
+        new CreateLastValueData(measure));
+  }
+
+  // Covert a mapping from TagValues to MutableAggregation, to a mapping from TagValues to
+  // AggregationData.
+  static <T> Map<T, AggregationData> createAggregationMap(
+      Map<T, MutableAggregation> tagValueAggregationMap, Measure measure) {
+    Map<T, AggregationData> map = Maps.newHashMap();
+    for (Entry<T, MutableAggregation> entry : tagValueAggregationMap.entrySet()) {
+      map.put(entry.getKey(), createAggregationData(entry.getValue(), measure));
+    }
+    return map;
+  }
+
+  static double getDoubleValueFromMeasurement(Measurement measurement) {
+    return measurement.match(
+        GET_VALUE_FROM_MEASUREMENT_DOUBLE,
+        GET_VALUE_FROM_MEASUREMENT_LONG,
+        Functions.</*@Nullable*/ Double>throwAssertionError());
+  }
+
+  // static inner Function classes
+
+  private static final Function<MeasurementDouble, Double> GET_VALUE_FROM_MEASUREMENT_DOUBLE =
+      new Function<MeasurementDouble, Double>() {
+        @Override
+        public Double apply(MeasurementDouble arg) {
+          return arg.getValue();
+        }
+      };
+
+  private static final Function<MeasurementLong, Double> GET_VALUE_FROM_MEASUREMENT_LONG =
+      new Function<MeasurementLong, Double>() {
+        @Override
+        public Double apply(MeasurementLong arg) {
+          // TODO: consider checking truncation here.
+          return (double) arg.getValue();
+        }
+      };
+
+  private static final class CreateMutableSum implements Function<Sum, MutableAggregation> {
+    @Override
+    public MutableAggregation apply(Sum arg) {
+      return MutableSum.create();
+    }
+
+    private static final CreateMutableSum INSTANCE = new CreateMutableSum();
+  }
+
+  private static final class CreateMutableCount implements Function<Count, MutableAggregation> {
+    @Override
+    public MutableAggregation apply(Count arg) {
+      return MutableCount.create();
+    }
+
+    private static final CreateMutableCount INSTANCE = new CreateMutableCount();
+  }
+
+  // TODO(songya): remove this once Mean aggregation is completely removed. Before that
+  // we need to continue supporting Mean, since it could still be used by users and some
+  // deprecated RPC views.
+  private static final class AggregationDefaultFunction
+      implements Function<Aggregation, MutableAggregation> {
+    @Override
+    public MutableAggregation apply(Aggregation arg) {
+      if (arg instanceof Aggregation.Mean) {
+        return MutableMean.create();
+      }
+      throw new IllegalArgumentException("Unknown Aggregation.");
+    }
+
+    private static final AggregationDefaultFunction INSTANCE = new AggregationDefaultFunction();
+  }
+
+  private static final class CreateMutableDistribution
+      implements Function<Distribution, MutableAggregation> {
+    @Override
+    public MutableAggregation apply(Distribution arg) {
+      return MutableDistribution.create(arg.getBucketBoundaries());
+    }
+
+    private static final CreateMutableDistribution INSTANCE = new CreateMutableDistribution();
+  }
+
+  private static final class CreateMutableLastValue
+      implements Function<LastValue, MutableAggregation> {
+    @Override
+    public MutableAggregation apply(LastValue arg) {
+      return MutableLastValue.create();
+    }
+
+    private static final CreateMutableLastValue INSTANCE = new CreateMutableLastValue();
+  }
+
+  private static final class CreateSumData implements Function<MutableSum, AggregationData> {
+
+    private final Measure measure;
+
+    private CreateSumData(Measure measure) {
+      this.measure = measure;
+    }
+
+    @Override
+    public AggregationData apply(final MutableSum arg) {
+      return measure.match(
+          Functions.<AggregationData>returnConstant(SumDataDouble.create(arg.getSum())),
+          Functions.<AggregationData>returnConstant(SumDataLong.create(Math.round(arg.getSum()))),
+          Functions.<AggregationData>throwAssertionError());
+    }
+  }
+
+  private static final class CreateCountData implements Function<MutableCount, AggregationData> {
+    @Override
+    public AggregationData apply(MutableCount arg) {
+      return CountData.create(arg.getCount());
+    }
+
+    private static final CreateCountData INSTANCE = new CreateCountData();
+  }
+
+  private static final class CreateMeanData implements Function<MutableMean, AggregationData> {
+    @Override
+    public AggregationData apply(MutableMean arg) {
+      return AggregationData.MeanData.create(arg.getMean(), arg.getCount());
+    }
+
+    private static final CreateMeanData INSTANCE = new CreateMeanData();
+  }
+
+  private static final class CreateDistributionData
+      implements Function<MutableDistribution, AggregationData> {
+    @Override
+    public AggregationData apply(MutableDistribution arg) {
+      List<Long> boxedBucketCounts = new ArrayList<Long>();
+      for (long bucketCount : arg.getBucketCounts()) {
+        boxedBucketCounts.add(bucketCount);
+      }
+      List<Exemplar> exemplars = new ArrayList<Exemplar>();
+      if (arg.getExemplars() != null) {
+        for (Exemplar exemplar : arg.getExemplars()) {
+          if (exemplar != null) {
+            exemplars.add(exemplar);
+          }
+        }
+      }
+      return DistributionData.create(
+          arg.getMean(),
+          arg.getCount(),
+          arg.getMin(),
+          arg.getMax(),
+          arg.getSumOfSquaredDeviations(),
+          boxedBucketCounts,
+          exemplars);
+    }
+
+    private static final CreateDistributionData INSTANCE = new CreateDistributionData();
+  }
+
+  private static final class CreateLastValueData
+      implements Function<MutableLastValue, AggregationData> {
+
+    private final Measure measure;
+
+    private CreateLastValueData(Measure measure) {
+      this.measure = measure;
+    }
+
+    @Override
+    public AggregationData apply(final MutableLastValue arg) {
+      return measure.match(
+          Functions.<AggregationData>returnConstant(LastValueDataDouble.create(arg.getLastValue())),
+          Functions.<AggregationData>returnConstant(
+              LastValueDataLong.create(Math.round(arg.getLastValue()))),
+          Functions.<AggregationData>throwAssertionError());
+    }
+  }
+
+  private RecordUtils() {}
+}
diff --git a/impl_core/src/test/java/io/opencensus/implcore/stats/MutableViewDataTest.java b/impl_core/src/test/java/io/opencensus/implcore/stats/MutableViewDataTest.java
index e397ad65..06f50fed 100644
--- a/impl_core/src/test/java/io/opencensus/implcore/stats/MutableViewDataTest.java
+++ b/impl_core/src/test/java/io/opencensus/implcore/stats/MutableViewDataTest.java
@@ -18,35 +18,7 @@ package io.opencensus.implcore.stats;
 
 import static com.google.common.truth.Truth.assertThat;
 
-import com.google.common.collect.ImmutableMap;
 import io.opencensus.common.Timestamp;
-import io.opencensus.implcore.stats.MutableAggregation.MutableCount;
-import io.opencensus.implcore.stats.MutableAggregation.MutableDistribution;
-import io.opencensus.implcore.stats.MutableAggregation.MutableLastValue;
-import io.opencensus.implcore.stats.MutableAggregation.MutableMean;
-import io.opencensus.implcore.stats.MutableAggregation.MutableSum;
-import io.opencensus.stats.Aggregation.Count;
-import io.opencensus.stats.Aggregation.Distribution;
-import io.opencensus.stats.Aggregation.LastValue;
-import io.opencensus.stats.Aggregation.Mean;
-import io.opencensus.stats.Aggregation.Sum;
-import io.opencensus.stats.AggregationData;
-import io.opencensus.stats.AggregationData.CountData;
-import io.opencensus.stats.AggregationData.DistributionData;
-import io.opencensus.stats.AggregationData.LastValueDataDouble;
-import io.opencensus.stats.AggregationData.LastValueDataLong;
-import io.opencensus.stats.AggregationData.MeanData;
-import io.opencensus.stats.AggregationData.SumDataDouble;
-import io.opencensus.stats.AggregationData.SumDataLong;
-import io.opencensus.stats.BucketBoundaries;
-import io.opencensus.stats.Measure.MeasureDouble;
-import io.opencensus.stats.Measure.MeasureLong;
-import io.opencensus.tags.TagKey;
-import io.opencensus.tags.TagValue;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.List;
-import java.util.Map;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -55,94 +27,8 @@ import org.junit.runners.JUnit4;
 @RunWith(JUnit4.class)
 public class MutableViewDataTest {
 
-  private static final double EPSILON = 1e-7;
-
-  private static final TagKey ORIGINATOR = TagKey.create("originator");
-  private static final TagKey CALLER = TagKey.create("caller");
-  private static final TagKey METHOD = TagKey.create("method");
-  private static final TagValue CALLER_V = TagValue.create("some caller");
-  private static final TagValue METHOD_V = TagValue.create("some method");
-  private static final MeasureDouble MEASURE_DOUBLE =
-      MeasureDouble.create("measure1", "description", "1");
-  private static final MeasureLong MEASURE_LONG =
-      MeasureLong.create("measure2", "description", "1");
-
   @Test
   public void testConstants() {
-    assertThat(MutableViewData.UNKNOWN_TAG_VALUE).isNull();
     assertThat(MutableViewData.ZERO_TIMESTAMP).isEqualTo(Timestamp.create(0, 0));
   }
-
-  @Test
-  public void testGetTagValues() {
-    List<TagKey> columns = Arrays.asList(CALLER, METHOD, ORIGINATOR);
-    Map<TagKey, TagValue> tags = ImmutableMap.of(CALLER, CALLER_V, METHOD, METHOD_V);
-
-    assertThat(MutableViewData.getTagValues(tags, columns))
-        .containsExactly(CALLER_V, METHOD_V, MutableViewData.UNKNOWN_TAG_VALUE)
-        .inOrder();
-  }
-
-  @Test
-  public void createMutableAggregation() {
-    BucketBoundaries bucketBoundaries = BucketBoundaries.create(Arrays.asList(-1.0, 0.0, 1.0));
-
-    assertThat(((MutableSum) MutableViewData.createMutableAggregation(Sum.create())).getSum())
-        .isWithin(EPSILON)
-        .of(0.0);
-    assertThat(((MutableCount) MutableViewData.createMutableAggregation(Count.create())).getCount())
-        .isEqualTo(0L);
-    assertThat(((MutableMean) MutableViewData.createMutableAggregation(Mean.create())).getMean())
-        .isWithin(EPSILON)
-        .of(0D);
-    assertThat(
-            ((MutableLastValue) MutableViewData.createMutableAggregation(LastValue.create()))
-                .getLastValue())
-        .isNaN();
-
-    MutableDistribution mutableDistribution =
-        (MutableDistribution)
-            MutableViewData.createMutableAggregation(Distribution.create(bucketBoundaries));
-    assertThat(mutableDistribution.getMin()).isPositiveInfinity();
-    assertThat(mutableDistribution.getMax()).isNegativeInfinity();
-    assertThat(mutableDistribution.getSumOfSquaredDeviations()).isWithin(EPSILON).of(0);
-    assertThat(mutableDistribution.getBucketCounts()).isEqualTo(new long[4]);
-  }
-
-  @Test
-  public void createAggregationData() {
-    BucketBoundaries bucketBoundaries = BucketBoundaries.create(Arrays.asList(-1.0, 0.0, 1.0));
-    List<AggregationData> aggregates = new ArrayList<AggregationData>();
-    aggregates.add(MutableViewData.createAggregationData(MutableSum.create(), MEASURE_DOUBLE));
-    aggregates.add(MutableViewData.createAggregationData(MutableSum.create(), MEASURE_LONG));
-    aggregates.add(
-        MutableViewData.createAggregationData(MutableLastValue.create(), MEASURE_DOUBLE));
-    aggregates.add(MutableViewData.createAggregationData(MutableLastValue.create(), MEASURE_LONG));
-
-    List<MutableAggregation> mutableAggregations =
-        Arrays.asList(
-            MutableCount.create(),
-            MutableMean.create(),
-            MutableDistribution.create(bucketBoundaries));
-    for (MutableAggregation mutableAggregation : mutableAggregations) {
-      aggregates.add(MutableViewData.createAggregationData(mutableAggregation, MEASURE_DOUBLE));
-    }
-
-    assertThat(aggregates)
-        .containsExactly(
-            SumDataDouble.create(0),
-            SumDataLong.create(0),
-            LastValueDataDouble.create(Double.NaN),
-            LastValueDataLong.create(0),
-            CountData.create(0),
-            MeanData.create(0, 0),
-            DistributionData.create(
-                0,
-                0,
-                Double.POSITIVE_INFINITY,
-                Double.NEGATIVE_INFINITY,
-                0,
-                Arrays.asList(new Long[] {0L, 0L, 0L, 0L})))
-        .inOrder();
-  }
 }
diff --git a/impl_core/src/test/java/io/opencensus/implcore/stats/RecordUtilsTest.java b/impl_core/src/test/java/io/opencensus/implcore/stats/RecordUtilsTest.java
new file mode 100644
index 00000000..7a4b1b3d
--- /dev/null
+++ b/impl_core/src/test/java/io/opencensus/implcore/stats/RecordUtilsTest.java
@@ -0,0 +1,144 @@
+/*
+ * Copyright 2018, OpenCensus Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.opencensus.implcore.stats;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableMap;
+import io.opencensus.implcore.stats.MutableAggregation.MutableCount;
+import io.opencensus.implcore.stats.MutableAggregation.MutableDistribution;
+import io.opencensus.implcore.stats.MutableAggregation.MutableLastValue;
+import io.opencensus.implcore.stats.MutableAggregation.MutableMean;
+import io.opencensus.implcore.stats.MutableAggregation.MutableSum;
+import io.opencensus.stats.Aggregation.Count;
+import io.opencensus.stats.Aggregation.Distribution;
+import io.opencensus.stats.Aggregation.LastValue;
+import io.opencensus.stats.Aggregation.Mean;
+import io.opencensus.stats.Aggregation.Sum;
+import io.opencensus.stats.AggregationData;
+import io.opencensus.stats.AggregationData.CountData;
+import io.opencensus.stats.AggregationData.DistributionData;
+import io.opencensus.stats.AggregationData.LastValueDataDouble;
+import io.opencensus.stats.AggregationData.LastValueDataLong;
+import io.opencensus.stats.AggregationData.MeanData;
+import io.opencensus.stats.AggregationData.SumDataDouble;
+import io.opencensus.stats.AggregationData.SumDataLong;
+import io.opencensus.stats.BucketBoundaries;
+import io.opencensus.stats.Measure.MeasureDouble;
+import io.opencensus.stats.Measure.MeasureLong;
+import io.opencensus.tags.TagKey;
+import io.opencensus.tags.TagValue;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Tests for {@link RecordUtils}. */
+@RunWith(JUnit4.class)
+public class RecordUtilsTest {
+
+  private static final double EPSILON = 1e-7;
+  private static final MeasureDouble MEASURE_DOUBLE =
+      MeasureDouble.create("measure1", "description", "1");
+  private static final MeasureLong MEASURE_LONG =
+      MeasureLong.create("measure2", "description", "1");
+  private static final TagKey ORIGINATOR = TagKey.create("originator");
+  private static final TagKey CALLER = TagKey.create("caller");
+  private static final TagKey METHOD = TagKey.create("method");
+  private static final TagValue CALLER_V = TagValue.create("some caller");
+  private static final TagValue METHOD_V = TagValue.create("some method");
+
+  @Test
+  public void testConstants() {
+    assertThat(RecordUtils.UNKNOWN_TAG_VALUE).isNull();
+  }
+
+  @Test
+  public void testGetTagValues() {
+    List<TagKey> columns = Arrays.asList(CALLER, METHOD, ORIGINATOR);
+    Map<TagKey, TagValue> tags = ImmutableMap.of(CALLER, CALLER_V, METHOD, METHOD_V);
+
+    assertThat(RecordUtils.getTagValues(tags, columns))
+        .containsExactly(CALLER_V, METHOD_V, RecordUtils.UNKNOWN_TAG_VALUE)
+        .inOrder();
+  }
+
+  @Test
+  public void createMutableAggregation() {
+    BucketBoundaries bucketBoundaries = BucketBoundaries.create(Arrays.asList(-1.0, 0.0, 1.0));
+
+    assertThat(((MutableSum) RecordUtils.createMutableAggregation(Sum.create())).getSum())
+        .isWithin(EPSILON)
+        .of(0.0);
+    assertThat(((MutableCount) RecordUtils.createMutableAggregation(Count.create())).getCount())
+        .isEqualTo(0L);
+    assertThat(((MutableMean) RecordUtils.createMutableAggregation(Mean.create())).getMean())
+        .isWithin(EPSILON)
+        .of(0D);
+    assertThat(
+            ((MutableLastValue) RecordUtils.createMutableAggregation(LastValue.create()))
+                .getLastValue())
+        .isNaN();
+
+    MutableDistribution mutableDistribution =
+        (MutableDistribution)
+            RecordUtils.createMutableAggregation(Distribution.create(bucketBoundaries));
+    assertThat(mutableDistribution.getMin()).isPositiveInfinity();
+    assertThat(mutableDistribution.getMax()).isNegativeInfinity();
+    assertThat(mutableDistribution.getSumOfSquaredDeviations()).isWithin(EPSILON).of(0);
+    assertThat(mutableDistribution.getBucketCounts()).isEqualTo(new long[4]);
+  }
+
+  @Test
+  public void createAggregationData() {
+    BucketBoundaries bucketBoundaries = BucketBoundaries.create(Arrays.asList(-1.0, 0.0, 1.0));
+    List<AggregationData> aggregates = new ArrayList<AggregationData>();
+    aggregates.add(RecordUtils.createAggregationData(MutableSum.create(), MEASURE_DOUBLE));
+    aggregates.add(RecordUtils.createAggregationData(MutableSum.create(), MEASURE_LONG));
+    aggregates.add(RecordUtils.createAggregationData(MutableLastValue.create(), MEASURE_DOUBLE));
+    aggregates.add(RecordUtils.createAggregationData(MutableLastValue.create(), MEASURE_LONG));
+
+    List<MutableAggregation> mutableAggregations =
+        Arrays.asList(
+            MutableCount.create(),
+            MutableMean.create(),
+            MutableDistribution.create(bucketBoundaries));
+    for (MutableAggregation mutableAggregation : mutableAggregations) {
+      aggregates.add(RecordUtils.createAggregationData(mutableAggregation, MEASURE_DOUBLE));
+    }
+
+    assertThat(aggregates)
+        .containsExactly(
+            SumDataDouble.create(0),
+            SumDataLong.create(0),
+            LastValueDataDouble.create(Double.NaN),
+            LastValueDataLong.create(0),
+            CountData.create(0),
+            MeanData.create(0, 0),
+            DistributionData.create(
+                0,
+                0,
+                Double.POSITIVE_INFINITY,
+                Double.NEGATIVE_INFINITY,
+                0,
+                Arrays.asList(0L, 0L, 0L, 0L)))
+        .inOrder();
+  }
+}
diff --git a/impl_core/src/test/java/io/opencensus/implcore/stats/StatsRecorderImplTest.java b/impl_core/src/test/java/io/opencensus/implcore/stats/StatsRecorderImplTest.java
index 3c8d7af3..bd8b5b88 100644
--- a/impl_core/src/test/java/io/opencensus/implcore/stats/StatsRecorderImplTest.java
+++ b/impl_core/src/test/java/io/opencensus/implcore/stats/StatsRecorderImplTest.java
@@ -21,11 +21,11 @@ import static io.opencensus.implcore.stats.MutableViewData.ZERO_TIMESTAMP;
 import static io.opencensus.implcore.stats.StatsTestUtil.createEmptyViewData;
 
 import com.google.common.collect.ImmutableMap;
-import com.google.common.collect.Lists;
 import io.grpc.Context;
 import io.opencensus.common.Duration;
 import io.opencensus.common.Timestamp;
 import io.opencensus.implcore.internal.SimpleEventQueue;
+import io.opencensus.implcore.stats.StatsTestUtil.SimpleTagContext;
 import io.opencensus.stats.Aggregation.Count;
 import io.opencensus.stats.Aggregation.Distribution;
 import io.opencensus.stats.Aggregation.Sum;
@@ -51,7 +51,6 @@ import io.opencensus.tags.unsafe.ContextUtils;
 import io.opencensus.testing.common.TestClock;
 import java.util.Arrays;
 import java.util.Collections;
-import java.util.Iterator;
 import java.util.List;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -347,17 +346,4 @@ public final class StatsRecorderImplTest {
             StatsTestUtil.createAggregationData(Sum.create(), MEASURE_DOUBLE, 4.0)),
         1e-6);
   }
-
-  private static final class SimpleTagContext extends TagContext {
-    private final List<Tag> tags;
-
-    SimpleTagContext(Tag... tags) {
-      this.tags = Collections.unmodifiableList(Lists.newArrayList(tags));
-    }
-
-    @Override
-    protected Iterator<Tag> getIterator() {
-      return tags.iterator();
-    }
-  }
 }
diff --git a/impl_core/src/test/java/io/opencensus/implcore/stats/StatsTestUtil.java b/impl_core/src/test/java/io/opencensus/implcore/stats/StatsTestUtil.java
index 6a2e6366..ec436d22 100644
--- a/impl_core/src/test/java/io/opencensus/implcore/stats/StatsTestUtil.java
+++ b/impl_core/src/test/java/io/opencensus/implcore/stats/StatsTestUtil.java
@@ -20,6 +20,7 @@ import static com.google.common.truth.Truth.assertThat;
 import static io.opencensus.implcore.stats.MutableViewData.ZERO_TIMESTAMP;
 
 import com.google.common.collect.Iterables;
+import com.google.common.collect.Lists;
 import io.opencensus.common.Function;
 import io.opencensus.common.Functions;
 import io.opencensus.common.Timestamp;
@@ -38,9 +39,12 @@ import io.opencensus.stats.ViewData;
 import io.opencensus.stats.ViewData.AggregationWindowData;
 import io.opencensus.stats.ViewData.AggregationWindowData.CumulativeData;
 import io.opencensus.stats.ViewData.AggregationWindowData.IntervalData;
+import io.opencensus.tags.Tag;
+import io.opencensus.tags.TagContext;
 import io.opencensus.tags.TagValue;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -63,11 +67,11 @@ final class StatsTestUtil {
    */
   static AggregationData createAggregationData(
       Aggregation aggregation, Measure measure, double... values) {
-    MutableAggregation mutableAggregation = MutableViewData.createMutableAggregation(aggregation);
+    MutableAggregation mutableAggregation = RecordUtils.createMutableAggregation(aggregation);
     for (double value : values) {
       mutableAggregation.add(value, Collections.<String, String>emptyMap(), EMPTY);
     }
-    return MutableViewData.createAggregationData(mutableAggregation, measure);
+    return RecordUtils.createAggregationData(mutableAggregation, measure);
   }
 
   /**
@@ -211,4 +215,17 @@ final class StatsTestUtil {
     }
     return truncated;
   }
+
+  static final class SimpleTagContext extends TagContext {
+    private final List<Tag> tags;
+
+    SimpleTagContext(Tag... tags) {
+      this.tags = Collections.unmodifiableList(Lists.newArrayList(tags));
+    }
+
+    @Override
+    protected Iterator<Tag> getIterator() {
+      return tags.iterator();
+    }
+  }
 }
diff --git a/impl_core/src/test/java/io/opencensus/implcore/stats/ViewManagerImplTest.java b/impl_core/src/test/java/io/opencensus/implcore/stats/ViewManagerImplTest.java
index 270d65c0..b3ec6f2d 100644
--- a/impl_core/src/test/java/io/opencensus/implcore/stats/ViewManagerImplTest.java
+++ b/impl_core/src/test/java/io/opencensus/implcore/stats/ViewManagerImplTest.java
@@ -634,7 +634,7 @@ public class ViewManagerImplTest {
         ImmutableMap.of(
             // Tag is missing for associated measureValues, should use default tag value
             // "unknown/not set".
-            Arrays.asList(MutableViewData.UNKNOWN_TAG_VALUE),
+            Arrays.asList(RecordUtils.UNKNOWN_TAG_VALUE),
             // Should record stats with default tag value: "KEY" : "unknown/not set".
             createAggregationData(DISTRIBUTION, MEASURE_DOUBLE, 10.0)),
         EPSILON);
@@ -682,7 +682,7 @@ public class ViewManagerImplTest {
         ImmutableMap.of(
             // Won't record the unregistered tag key, for missing registered keys will use default
             // tag value : "unknown/not set".
-            Arrays.asList(MutableViewData.UNKNOWN_TAG_VALUE),
+            Arrays.asList(RecordUtils.UNKNOWN_TAG_VALUE),
             // Should record stats with default tag value: "KEY" : "unknown/not set".
             createAggregationData(DISTRIBUTION, MEASURE_DOUBLE, 10.0, 50.0)),
         EPSILON);