Merge pull request #564 from sebright/tag-value-class

Add a TagValue class.

28 files changed, 486 insertions, 252 deletions

diff --git a/core/src/main/java/io/opencensus/stats/ViewData.java b/core/src/main/java/io/opencensus/stats/ViewData.java
index 39138f59..9f4a4d1b 100644
--- a/core/src/main/java/io/opencensus/stats/ViewData.java
+++ b/core/src/main/java/io/opencensus/stats/ViewData.java
@@ -20,7 +20,7 @@ import com.google.auto.value.AutoValue;
 import io.opencensus.common.Function;
 import io.opencensus.common.Functions;
 import io.opencensus.common.Timestamp;
-
+import io.opencensus.tags.TagValue;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
@@ -45,8 +45,7 @@ public abstract class ViewData {
    * The {@link AggregationData}s grouped by combination of tag values, associated with this
    * {@link ViewData}.
    */
-  // TODO(sebright): Create a TagValue class.
-  public abstract Map<List<Object>, List<AggregationData>> getAggregationMap();
+  public abstract Map<List<TagValue>, List<AggregationData>> getAggregationMap();
 
   /**
    * Returns the {@link WindowData} associated with this {@link ViewData}.
@@ -58,7 +57,7 @@ public abstract class ViewData {
   /** Constructs a new {@link ViewData}. */
   public static ViewData create(
       View view,
-      Map<? extends List<? extends Object>, List<AggregationData>> map,
+      Map<? extends List<? extends TagValue>, List<AggregationData>> map,
       final WindowData windowData) {
     view.getWindow()
         .match(
@@ -92,11 +91,11 @@ public abstract class ViewData {
             },
             Functions.<Void>throwIllegalArgumentException());
 
-    Map<List<Object>, List<AggregationData>> deepCopy =
-        new HashMap<List<Object>, List<AggregationData>>();
-    for (Entry<? extends List<? extends Object>, List<AggregationData>> entry : map.entrySet()) {
+    Map<List<TagValue>, List<AggregationData>> deepCopy =
+        new HashMap<List<TagValue>, List<AggregationData>>();
+    for (Entry<? extends List<? extends TagValue>, List<AggregationData>> entry : map.entrySet()) {
       deepCopy.put(
-          Collections.unmodifiableList(new ArrayList<Object>(entry.getKey())),
+          Collections.unmodifiableList(new ArrayList<TagValue>(entry.getKey())),
           Collections.unmodifiableList(new ArrayList<AggregationData>(entry.getValue())));
     }
 
diff --git a/core/src/main/java/io/opencensus/tags/Tag.java b/core/src/main/java/io/opencensus/tags/Tag.java
index 3450fb58..a53cd838 100644
--- a/core/src/main/java/io/opencensus/tags/Tag.java
+++ b/core/src/main/java/io/opencensus/tags/Tag.java
@@ -21,6 +21,9 @@ import io.opencensus.common.Function;
 import io.opencensus.tags.TagKey.TagKeyBoolean;
 import io.opencensus.tags.TagKey.TagKeyLong;
 import io.opencensus.tags.TagKey.TagKeyString;
+import io.opencensus.tags.TagValue.TagValueBoolean;
+import io.opencensus.tags.TagValue.TagValueLong;
+import io.opencensus.tags.TagValue.TagValueString;
 import javax.annotation.concurrent.Immutable;
 
 /** {@link TagKey} paired with a value. */
@@ -35,6 +38,15 @@ public abstract class Tag {
   public abstract TagKey getKey();
 
   /**
+   * Returns the associated tag value.
+   *
+   * @return the associated tag value.
+   */
+  public abstract TagValue getValue();
+
+  Tag() {}
+
+  /**
    * Applies a function to the tag's key and value. The function that is called depends on the type
    * of the tag. This is similar to the visitor pattern. {@code match} also takes a function to
    * handle the default case, for backwards compatibility when tag types are added. For example,
@@ -115,11 +127,7 @@ public abstract class Tag {
     @Override
     public abstract TagKeyString getKey();
 
-    /**
-     * Returns the associated tag value.
-     *
-     * @return the associated tag value.
-     */
+    @Override
     public abstract TagValueString getValue();
 
     @Override
@@ -145,19 +153,15 @@ public abstract class Tag {
      * @param value the tag value.
      * @return a {@code TagLong} with the given key and value.
      */
-    public static TagLong create(TagKeyLong key, long value) {
+    public static TagLong create(TagKeyLong key, TagValueLong value) {
       return new AutoValue_Tag_TagLong(key, value);
     }
 
     @Override
     public abstract TagKeyLong getKey();
 
-    /**
-     * Returns the associated tag value.
-     *
-     * @return the associated tag value.
-     */
-    public abstract long getValue();
+    @Override
+    public abstract TagValueLong getValue();
 
     @Override
     public final <T> T match(
@@ -182,19 +186,15 @@ public abstract class Tag {
      * @param value the tag value.
      * @return a {@code TagBoolean} with the given key and value.
      */
-    public static TagBoolean create(TagKeyBoolean key, boolean value) {
+    public static TagBoolean create(TagKeyBoolean key, TagValueBoolean value) {
       return new AutoValue_Tag_TagBoolean(key, value);
     }
 
     @Override
     public abstract TagKeyBoolean getKey();
 
-    /**
-     * Returns the associated tag value.
-     *
-     * @return the associated tag value.
-     */
-    public abstract boolean getValue();
+    @Override
+    public abstract TagValueBoolean getValue();
 
     @Override
     public final <T> T match(
diff --git a/core/src/main/java/io/opencensus/tags/TagContext.java b/core/src/main/java/io/opencensus/tags/TagContext.java
index 5f40bee4..5743701a 100644
--- a/core/src/main/java/io/opencensus/tags/TagContext.java
+++ b/core/src/main/java/io/opencensus/tags/TagContext.java
@@ -16,6 +16,7 @@
 
 package io.opencensus.tags;
 
+import io.opencensus.tags.TagValue.TagValueString;
 import java.util.Collections;
 import java.util.Iterator;
 import javax.annotation.concurrent.Immutable;
diff --git a/core/src/main/java/io/opencensus/tags/TagContextBuilder.java b/core/src/main/java/io/opencensus/tags/TagContextBuilder.java
index 56efd210..f86d10b3 100644
--- a/core/src/main/java/io/opencensus/tags/TagContextBuilder.java
+++ b/core/src/main/java/io/opencensus/tags/TagContextBuilder.java
@@ -20,6 +20,9 @@ import io.opencensus.common.Scope;
 import io.opencensus.tags.TagKey.TagKeyBoolean;
 import io.opencensus.tags.TagKey.TagKeyLong;
 import io.opencensus.tags.TagKey.TagKeyString;
+import io.opencensus.tags.TagValue.TagValueBoolean;
+import io.opencensus.tags.TagValue.TagValueLong;
+import io.opencensus.tags.TagValue.TagValueString;
 import javax.annotation.concurrent.Immutable;
 
 /** Builder for the {@link TagContext} class. */
@@ -44,7 +47,7 @@ public abstract class TagContextBuilder {
    * @param value the value to set for the given key.
    * @return this
    */
-  public abstract TagContextBuilder set(TagKeyLong key, long value);
+  public abstract TagContextBuilder set(TagKeyLong key, TagValueLong value);
 
   /**
    * Adds the key/value pair regardless of whether the key is present.
@@ -53,7 +56,7 @@ public abstract class TagContextBuilder {
    * @param value the value to set for the given key.
    * @return this
    */
-  public abstract TagContextBuilder set(TagKeyBoolean key, boolean value);
+  public abstract TagContextBuilder set(TagKeyBoolean key, TagValueBoolean value);
 
   /**
    * Removes the key if it exists.
@@ -100,12 +103,12 @@ public abstract class TagContextBuilder {
     }
 
     @Override
-    public TagContextBuilder set(TagKeyLong key, long value) {
+    public TagContextBuilder set(TagKeyLong key, TagValueLong value) {
       return this;
     }
 
     @Override
-    public TagContextBuilder set(TagKeyBoolean key, boolean value) {
+    public TagContextBuilder set(TagKeyBoolean key, TagValueBoolean value) {
       return this;
     }
 
diff --git a/core/src/main/java/io/opencensus/tags/TagKey.java b/core/src/main/java/io/opencensus/tags/TagKey.java
index aa125bf3..943f12d7 100644
--- a/core/src/main/java/io/opencensus/tags/TagKey.java
+++ b/core/src/main/java/io/opencensus/tags/TagKey.java
@@ -21,6 +21,7 @@ import static com.google.common.base.Preconditions.checkArgument;
 import com.google.auto.value.AutoValue;
 import io.opencensus.common.Function;
 import io.opencensus.internal.StringUtil;
+import io.opencensus.tags.TagValue.TagValueString;
 import javax.annotation.concurrent.Immutable;
 
 /**
diff --git a/core/src/main/java/io/opencensus/tags/TagValue.java b/core/src/main/java/io/opencensus/tags/TagValue.java
new file mode 100644
index 00000000..7da713c5
--- /dev/null
+++ b/core/src/main/java/io/opencensus/tags/TagValue.java
@@ -0,0 +1,182 @@
+/*
+ * Copyright 2017, 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.tags;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.base.Preconditions;
+import io.opencensus.common.Function;
+import io.opencensus.internal.StringUtil;
+import io.opencensus.tags.TagKey.TagKeyBoolean;
+import io.opencensus.tags.TagKey.TagKeyLong;
+import io.opencensus.tags.TagKey.TagKeyString;
+import javax.annotation.concurrent.Immutable;
+
+/** A validated tag value. */
+@Immutable
+public abstract class TagValue {
+
+  TagValue() {}
+
+  /**
+   * Applies a function to a tag value. The function that is called depends on the type of the
+   * value. This is similar to the visitor pattern. {@code match} also takes a function to handle
+   * the default case, for backwards compatibility when tag types are added.
+   *
+   * @param stringFunction the function to call when the tag value has type {@code String}.
+   * @param longFunction the function to call when the tag value has type {@code long}.
+   * @param booleanFunction the function to call when the tag value has type {@code boolean}.
+   * @param defaultFunction the function to call when the tag value has a type other than {@code
+   *     String}, {@code long}, or {@code boolean}.
+   * @param <T> The result type of the function.
+   * @return The result of calling the function that matches the tag value's type.
+   */
+  public abstract <T> T match(
+      Function<? super TagValueString, T> stringFunction,
+      Function<? super TagValueLong, T> longFunction,
+      Function<? super TagValueBoolean, T> booleanFunction,
+      Function<? super TagValue, T> defaultFunction);
+
+  /**
+   * A validated tag value associated with a {@link TagKeyString}.
+   *
+   * <p>Validation ensures that the {@code String} has a maximum length of {@link #MAX_LENGTH} and
+   * contains only printable ASCII characters.
+   */
+  @Immutable
+  @AutoValue
+  public abstract static class TagValueString extends TagValue {
+    /** The maximum length for a {@code String} tag value. The value is {@value #MAX_LENGTH}. */
+    public static final int MAX_LENGTH = 256;
+
+    TagValueString() {}
+
+    /**
+     * Constructs a {@code TagValueString} from the given string. The string must meet the following
+     * requirements:
+     *
+     * <ol>
+     *   <li>It cannot be longer than {@link #MAX_LENGTH}.
+     *   <li>It can only contain printable ASCII characters.
+     * </ol>
+     *
+     * @param value the tag value.
+     * @throws IllegalArgumentException if the {@code String} is not valid.
+     */
+    public static TagValueString create(String value) {
+      Preconditions.checkArgument(isValid(value));
+      return new AutoValue_TagValue_TagValueString(value);
+    }
+
+    @Override
+    public final <T> T match(
+        Function<? super TagValueString, T> stringFunction,
+        Function<? super TagValueLong, T> longFunction,
+        Function<? super TagValueBoolean, T> booleanFunction,
+        Function<? super TagValue, T> defaultFunction) {
+      return stringFunction.apply(this);
+    }
+
+    /**
+     * Returns the tag value as a {@code String}.
+     *
+     * @return the tag value as a {@code String}.
+     */
+    public abstract String asString();
+
+    /**
+     * Determines whether the given {@code String} is a valid tag value.
+     *
+     * @param value the tag value to be validated.
+     * @return whether the value is valid.
+     */
+    private static boolean isValid(String value) {
+      return value.length() <= MAX_LENGTH && StringUtil.isPrintableString(value);
+    }
+  }
+
+  /** A tag value associated with a {@link TagKeyLong}. */
+  @Immutable
+  @AutoValue
+  public abstract static class TagValueLong extends TagValue {
+
+    TagValueLong() {}
+
+    /**
+     * Constructs a {@code TagValueLong} from the given {@code long}.
+     *
+     * @param value the tag value.
+     */
+    public static TagValueLong create(long value) {
+      return new AutoValue_TagValue_TagValueLong(value);
+    }
+
+    @Override
+    public final <T> T match(
+        Function<? super TagValueString, T> stringFunction,
+        Function<? super TagValueLong, T> longFunction,
+        Function<? super TagValueBoolean, T> booleanFunction,
+        Function<? super TagValue, T> defaultFunction) {
+      return longFunction.apply(this);
+    }
+
+    /**
+     * Returns the tag value as a {@code long}.
+     *
+     * @return the tag value as a {@code long}.
+     */
+    public abstract long asLong();
+  }
+
+  /** A tag value associated with a {@link TagKeyBoolean}. */
+  @Immutable
+  @AutoValue
+  public abstract static class TagValueBoolean extends TagValue {
+    private static final TagValueBoolean TRUE_VALUE = createInternal(true);
+    private static final TagValueBoolean FALSE_VALUE = createInternal(false);
+
+    TagValueBoolean() {}
+
+    /**
+     * Constructs a {@code TagValueBoolean} from the given {@code boolean}.
+     *
+     * @param value the tag value.
+     */
+    public static TagValueBoolean create(boolean value) {
+      return value ? TRUE_VALUE : FALSE_VALUE;
+    }
+
+    private static TagValueBoolean createInternal(boolean value) {
+      return new AutoValue_TagValue_TagValueBoolean(value);
+    }
+
+    @Override
+    public final <T> T match(
+        Function<? super TagValueString, T> stringFunction,
+        Function<? super TagValueLong, T> longFunction,
+        Function<? super TagValueBoolean, T> booleanFunction,
+        Function<? super TagValue, T> defaultFunction) {
+      return booleanFunction.apply(this);
+    }
+
+    /**
+     * Returns the tag value as a {@code boolean}.
+     *
+     * @return the tag value as a {@code boolean}.
+     */
+    public abstract boolean asBoolean();
+  }
+}
diff --git a/core/src/main/java/io/opencensus/tags/TagValueString.java b/core/src/main/java/io/opencensus/tags/TagValueString.java
deleted file mode 100644
index 96d14d8f..00000000
--- a/core/src/main/java/io/opencensus/tags/TagValueString.java
+++ /dev/null
@@ -1,72 +0,0 @@
-/*
- * Copyright 2017, 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.tags;
-
-import com.google.auto.value.AutoValue;
-import com.google.common.base.Preconditions;
-import io.opencensus.internal.StringUtil;
-import io.opencensus.tags.TagKey.TagKeyString;
-import javax.annotation.concurrent.Immutable;
-
-/**
- * A validated tag value associated with a {@link TagKeyString}.
- *
- * <p>Validation ensures that the {@code String} has a maximum length of {@link #MAX_LENGTH} and
- * contains only printable ASCII characters.
- */
-@Immutable
-@AutoValue
-public abstract class TagValueString {
-  /** The maximum length for a {@code String} tag value. The value is {@value #MAX_LENGTH}. */
-  public static final int MAX_LENGTH = 255;
-
-  TagValueString() {}
-
-  /**
-   * Constructs a {@code TagValueString} from the given string. The string must meet the following
-   * requirements:
-   *
-   * <ol>
-   *   <li>It cannot be longer than {@link #MAX_LENGTH}.
-   *   <li>It can only contain printable ASCII characters.
-   * </ol>
-   *
-   * @param value the tag value.
-   * @throws IllegalArgumentException if the {@code String} is not valid.
-   */
-  public static TagValueString create(String value) {
-    Preconditions.checkArgument(isValid(value));
-    return new AutoValue_TagValueString(value);
-  }
-
-  /**
-   * Returns the tag value as a {@code String}.
-   *
-   * @return the tag value as a {@code String}.
-   */
-  public abstract String asString();
-
-  /**
-   * Determines whether the given {@code String} is a valid tag value.
-   *
-   * @param name the tag value to be validated.
-   * @return whether the value is valid.
-   */
-  private static boolean isValid(String name) {
-    return name.length() <= MAX_LENGTH && StringUtil.isPrintableString(name);
-  }
-}
diff --git a/core/src/test/java/io/opencensus/stats/NoopStatsRecorderTest.java b/core/src/test/java/io/opencensus/stats/NoopStatsRecorderTest.java
index 9e008755..9f92f3f9 100644
--- a/core/src/test/java/io/opencensus/stats/NoopStatsRecorderTest.java
+++ b/core/src/test/java/io/opencensus/stats/NoopStatsRecorderTest.java
@@ -21,7 +21,7 @@ import io.opencensus.tags.Tag;
 import io.opencensus.tags.Tag.TagString;
 import io.opencensus.tags.TagContext;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue.TagValueString;
 import java.util.Collections;
 import java.util.Iterator;
 import org.junit.Rule;
diff --git a/core/src/test/java/io/opencensus/stats/StatsRecorderTest.java b/core/src/test/java/io/opencensus/stats/StatsRecorderTest.java
index fd9b1d18..8835bf32 100644
--- a/core/src/test/java/io/opencensus/stats/StatsRecorderTest.java
+++ b/core/src/test/java/io/opencensus/stats/StatsRecorderTest.java
@@ -25,7 +25,7 @@ import io.opencensus.tags.Tag;
 import io.opencensus.tags.Tag.TagString;
 import io.opencensus.tags.TagContext;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue.TagValueString;
 import io.opencensus.tags.unsafe.ContextUtils;
 import java.util.Collections;
 import java.util.Iterator;
diff --git a/core/src/test/java/io/opencensus/stats/ViewDataTest.java b/core/src/test/java/io/opencensus/stats/ViewDataTest.java
index ab7b9917..e39b80e4 100644
--- a/core/src/test/java/io/opencensus/stats/ViewDataTest.java
+++ b/core/src/test/java/io/opencensus/stats/ViewDataTest.java
@@ -44,7 +44,8 @@ import io.opencensus.stats.ViewData.WindowData;
 import io.opencensus.stats.ViewData.WindowData.CumulativeData;
 import io.opencensus.stats.ViewData.WindowData.IntervalData;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue;
+import io.opencensus.tags.TagValue.TagValueString;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
@@ -119,7 +120,7 @@ public final class ViewDataTest {
                 IntervalData.create(Timestamp.fromMillis(2000))))
         .addEqualityGroup(
             ViewData.create(
-                intervalView, Collections.<List<Object>, List<AggregationData>>emptyMap(),
+                intervalView, Collections.<List<TagValue>, List<AggregationData>>emptyMap(),
                 IntervalData.create(Timestamp.fromMillis(2000))))
         .testEquals();
   }
diff --git a/core/src/test/java/io/opencensus/tags/CurrentTagContextUtilsTest.java b/core/src/test/java/io/opencensus/tags/CurrentTagContextUtilsTest.java
index 560c9e87..36b502d6 100644
--- a/core/src/test/java/io/opencensus/tags/CurrentTagContextUtilsTest.java
+++ b/core/src/test/java/io/opencensus/tags/CurrentTagContextUtilsTest.java
@@ -24,6 +24,7 @@ import io.grpc.Context;
 import io.opencensus.common.Scope;
 import io.opencensus.tags.Tag.TagString;
 import io.opencensus.tags.TagKey.TagKeyString;
+import io.opencensus.tags.TagValue.TagValueString;
 import io.opencensus.tags.unsafe.ContextUtils;
 import java.util.Iterator;
 import java.util.List;
diff --git a/core/src/test/java/io/opencensus/tags/ScopedTagContextsTest.java b/core/src/test/java/io/opencensus/tags/ScopedTagContextsTest.java
index d9d25fb1..5adbcfec 100644
--- a/core/src/test/java/io/opencensus/tags/ScopedTagContextsTest.java
+++ b/core/src/test/java/io/opencensus/tags/ScopedTagContextsTest.java
@@ -26,6 +26,9 @@ import io.opencensus.tags.Tag.TagString;
 import io.opencensus.tags.TagKey.TagKeyBoolean;
 import io.opencensus.tags.TagKey.TagKeyLong;
 import io.opencensus.tags.TagKey.TagKeyString;
+import io.opencensus.tags.TagValue.TagValueBoolean;
+import io.opencensus.tags.TagValue.TagValueLong;
+import io.opencensus.tags.TagValue.TagValueString;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
@@ -151,12 +154,12 @@ public class ScopedTagContextsTest {
     }
 
     @Override
-    public TagContextBuilder set(TagKeyLong key, long value) {
+    public TagContextBuilder set(TagKeyLong key, TagValueLong value) {
       throw new UnsupportedOperationException();
     }
 
     @Override
-    public TagContextBuilder set(TagKeyBoolean key, boolean value) {
+    public TagContextBuilder set(TagKeyBoolean key, TagValueBoolean value) {
       throw new UnsupportedOperationException();
     }
 
diff --git a/core/src/test/java/io/opencensus/tags/TagTest.java b/core/src/test/java/io/opencensus/tags/TagTest.java
index db2fd927..79b2eb4d 100644
--- a/core/src/test/java/io/opencensus/tags/TagTest.java
+++ b/core/src/test/java/io/opencensus/tags/TagTest.java
@@ -27,6 +27,9 @@ import io.opencensus.tags.Tag.TagString;
 import io.opencensus.tags.TagKey.TagKeyBoolean;
 import io.opencensus.tags.TagKey.TagKeyLong;
 import io.opencensus.tags.TagKey.TagKeyString;
+import io.opencensus.tags.TagValue.TagValueBoolean;
+import io.opencensus.tags.TagValue.TagValueLong;
+import io.opencensus.tags.TagValue.TagValueString;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -37,20 +40,19 @@ public final class TagTest {
 
   @Test
   public void testGetStringKey() {
-    assertThat(
-            TagString.create(TagKeyString.create("k"), TagValueString.create("v")).getKey())
+    assertThat(TagString.create(TagKeyString.create("k"), TagValueString.create("v")).getKey())
         .isEqualTo(TagKeyString.create("k"));
   }
 
   @Test
   public void testGetLongKey() {
-    assertThat(TagLong.create(TagKeyLong.create("k"), 2L).getKey())
+    assertThat(TagLong.create(TagKeyLong.create("k"), TagValueLong.create(2L)).getKey())
         .isEqualTo(TagKeyLong.create("k"));
   }
 
   @Test
   public void testGetBooleanKey() {
-    assertThat(TagBoolean.create(TagKeyBoolean.create("k"), false).getKey())
+    assertThat(TagBoolean.create(TagKeyBoolean.create("k"), TagValueBoolean.create(false)).getKey())
         .isEqualTo(TagKeyBoolean.create("k"));
   }
 
@@ -84,7 +86,7 @@ public final class TagTest {
   @Test
   public void testMatchLong() {
     assertThat(
-            TagLong.create(TagKeyLong.create("k2"), 3L)
+            TagLong.create(TagKeyLong.create("k2"), TagValueLong.create(3L))
                 .match(
                     new Function<TagString, Long>() {
                       @Override
@@ -95,7 +97,7 @@ public final class TagTest {
                     new Function<TagLong, Long>() {
                       @Override
                       public Long apply(TagLong tag) {
-                        return tag.getValue();
+                        return tag.getValue().asLong();
                       }
                     },
                     new Function<TagBoolean, Long>() {
@@ -111,7 +113,7 @@ public final class TagTest {
   @Test
   public void testMatchBoolean() {
     assertThat(
-            TagBoolean.create(TagKeyBoolean.create("k3"), false)
+            TagBoolean.create(TagKeyBoolean.create("k3"), TagValueBoolean.create(false))
                 .match(
                     new Function<TagString, Boolean>() {
                       @Override
@@ -128,7 +130,7 @@ public final class TagTest {
                     new Function<TagBoolean, Boolean>() {
                       @Override
                       public Boolean apply(TagBoolean tag) {
-                        return tag.getValue();
+                        return tag.getValue().asBoolean();
                       }
                     },
                     Functions.<Boolean>throwIllegalArgumentException()))
@@ -142,13 +144,15 @@ public final class TagTest {
             TagString.create(TagKeyString.create("Key1"), TagValueString.create("foo")),
             TagString.create(TagKeyString.create("Key1"), TagValueString.create("foo")))
         .addEqualityGroup(
-            TagLong.create(TagKeyLong.create("Key1"), 100L),
-            TagLong.create(TagKeyLong.create("Key1"), 100L))
+            TagLong.create(TagKeyLong.create("Key1"), TagValueLong.create(100L)),
+            TagLong.create(TagKeyLong.create("Key1"), TagValueLong.create(100L)))
+        .addEqualityGroup(
+            TagBoolean.create(TagKeyBoolean.create("Key1"), TagValueBoolean.create(true)),
+            TagBoolean.create(TagKeyBoolean.create("Key1"), TagValueBoolean.create(true)))
+        .addEqualityGroup(
+            TagBoolean.create(TagKeyBoolean.create("Key2"), TagValueBoolean.create(true)))
         .addEqualityGroup(
-            TagBoolean.create(TagKeyBoolean.create("Key1"), true),
-            TagBoolean.create(TagKeyBoolean.create("Key1"), true))
-        .addEqualityGroup(TagBoolean.create(TagKeyBoolean.create("Key2"), true))
-        .addEqualityGroup(TagBoolean.create(TagKeyBoolean.create("Key1"), false))
+            TagBoolean.create(TagKeyBoolean.create("Key1"), TagValueBoolean.create(false)))
         .testEquals();
   }
 }
diff --git a/core/src/test/java/io/opencensus/tags/TagValueStringTest.java b/core/src/test/java/io/opencensus/tags/TagValueStringTest.java
deleted file mode 100644
index fb997790..00000000
--- a/core/src/test/java/io/opencensus/tags/TagValueStringTest.java
+++ /dev/null
@@ -1,58 +0,0 @@
-/*
- * Copyright 2017, 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.tags;
-
-import static com.google.common.truth.Truth.assertThat;
-
-import io.opencensus.tags.TagValueString;
-import java.util.Arrays;
-import org.junit.Rule;
-import org.junit.Test;
-import org.junit.rules.ExpectedException;
-import org.junit.runner.RunWith;
-import org.junit.runners.JUnit4;
-
-/** Tests for {@link TagValueString}. */
-@RunWith(JUnit4.class)
-public class TagValueStringTest {
-
-  @Rule public final ExpectedException thrown = ExpectedException.none();
-
-  @Test
-  public void allowStringTagValueWithMaxLength() {
-    char[] chars = new char[TagValueString.MAX_LENGTH];
-    Arrays.fill(chars, 'v');
-    String value = new String(chars);
-    assertThat(TagValueString.create(value).asString()).isEqualTo(value);
-  }
-
-  @Test
-  public void disallowStringTagValueOverMaxLength() {
-    char[] chars = new char[TagValueString.MAX_LENGTH + 1];
-    Arrays.fill(chars, 'v');
-    String value = new String(chars);
-    thrown.expect(IllegalArgumentException.class);
-    TagValueString.create(value);
-  }
-
-  @Test
-  public void disallowStringTagValueWithUnprintableChars() {
-    String value = "\2ab\3cd";
-    thrown.expect(IllegalArgumentException.class);
-    TagValueString.create(value);
-  }
-}
diff --git a/core/src/test/java/io/opencensus/tags/TagValueTest.java b/core/src/test/java/io/opencensus/tags/TagValueTest.java
new file mode 100644
index 00000000..b1382312
--- /dev/null
+++ b/core/src/test/java/io/opencensus/tags/TagValueTest.java
@@ -0,0 +1,154 @@
+/*
+ * Copyright 2017, 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.tags;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.testing.EqualsTester;
+import io.opencensus.common.Function;
+import io.opencensus.common.Functions;
+import io.opencensus.tags.TagValue.TagValueBoolean;
+import io.opencensus.tags.TagValue.TagValueLong;
+import io.opencensus.tags.TagValue.TagValueString;
+import java.util.Arrays;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Tests for {@link TagValue}. */
+@RunWith(JUnit4.class)
+public final class TagValueTest {
+
+  @Rule public final ExpectedException thrown = ExpectedException.none();
+
+  @Test
+  public void testMatchStringValue() {
+    assertThat(
+            TagValueString.create("value")
+                .match(
+                    new Function<TagValueString, String>() {
+                      @Override
+                      public String apply(TagValueString tag) {
+                        return tag.asString();
+                      }
+                    },
+                    new Function<TagValueLong, String>() {
+                      @Override
+                      public String apply(TagValueLong tag) {
+                        throw new AssertionError();
+                      }
+                    },
+                    new Function<TagValueBoolean, String>() {
+                      @Override
+                      public String apply(TagValueBoolean tag) {
+                        throw new AssertionError();
+                      }
+                    },
+                    Functions.<String>throwIllegalArgumentException()))
+        .isEqualTo("value");
+  }
+
+  @Test
+  public void testMatchLongValue() {
+    assertThat(
+            TagValueLong.create(1234)
+                .match(
+                    new Function<TagValueString, Long>() {
+                      @Override
+                      public Long apply(TagValueString tag) {
+                        throw new AssertionError();
+                      }
+                    },
+                    new Function<TagValueLong, Long>() {
+                      @Override
+                      public Long apply(TagValueLong tag) {
+                        return tag.asLong();
+                      }
+                    },
+                    new Function<TagValueBoolean, Long>() {
+                      @Override
+                      public Long apply(TagValueBoolean tag) {
+                        throw new AssertionError();
+                      }
+                    },
+                    Functions.<Long>throwIllegalArgumentException()))
+        .isEqualTo(1234);
+  }
+
+  @Test
+  public void testMatchBooleanValue() {
+    assertThat(
+            TagValueBoolean.create(false)
+                .match(
+                    new Function<TagValueString, Boolean>() {
+                      @Override
+                      public Boolean apply(TagValueString tag) {
+                        throw new AssertionError();
+                      }
+                    },
+                    new Function<TagValueLong, Boolean>() {
+                      @Override
+                      public Boolean apply(TagValueLong tag) {
+                        throw new AssertionError();
+                      }
+                    },
+                    new Function<TagValueBoolean, Boolean>() {
+                      @Override
+                      public Boolean apply(TagValueBoolean tag) {
+                        return tag.asBoolean();
+                      }
+                    },
+                    Functions.<Boolean>throwIllegalArgumentException()))
+        .isEqualTo(false);
+  }
+
+  @Test
+  public void allowStringTagValueWithMaxLength() {
+    char[] chars = new char[TagValueString.MAX_LENGTH];
+    Arrays.fill(chars, 'v');
+    String value = new String(chars);
+    assertThat(TagValueString.create(value).asString()).isEqualTo(value);
+  }
+
+  @Test
+  public void disallowStringTagValueOverMaxLength() {
+    char[] chars = new char[TagValueString.MAX_LENGTH + 1];
+    Arrays.fill(chars, 'v');
+    String value = new String(chars);
+    thrown.expect(IllegalArgumentException.class);
+    TagValueString.create(value);
+  }
+
+  @Test
+  public void disallowStringTagValueWithUnprintableChars() {
+    String value = "\2ab\3cd";
+    thrown.expect(IllegalArgumentException.class);
+    TagValueString.create(value);
+  }
+
+  @Test
+  public void testTagValueEquals() {
+    new EqualsTester()
+        .addEqualityGroup(TagValueString.create("foo"), TagValueString.create("foo"))
+        .addEqualityGroup(TagValueLong.create(2))
+        .addEqualityGroup(TagValueBoolean.create(true))
+        .addEqualityGroup(TagValueString.create("bar"))
+        .testEquals();
+  }
+}
diff --git a/core_impl/src/main/java/io/opencensus/implcore/stats/MutableViewData.java b/core_impl/src/main/java/io/opencensus/implcore/stats/MutableViewData.java
index 8fcc9a42..aeefd498 100644
--- a/core_impl/src/main/java/io/opencensus/implcore/stats/MutableViewData.java
+++ b/core_impl/src/main/java/io/opencensus/implcore/stats/MutableViewData.java
@@ -55,6 +55,7 @@ import io.opencensus.tags.Tag.TagLong;
 import io.opencensus.tags.Tag.TagString;
 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;
@@ -67,36 +68,36 @@ import javax.annotation.Nullable;
  */
 final class MutableViewData {
 
-  private static final Function<TagString, Object> GET_STRING_TAG_VALUE =
-      new Function<TagString, Object>() {
+  private static final Function<TagString, TagValue> GET_STRING_TAG_VALUE =
+      new Function<TagString, TagValue>() {
         @Override
-        public Object apply(TagString tag) {
+        public TagValue apply(TagString tag) {
           return tag.getValue();
         }
       };
 
-  private static final Function<TagLong, Object> GET_LONG_TAG_VALUE =
-      new Function<TagLong, Object>() {
+  private static final Function<TagLong, TagValue> GET_LONG_TAG_VALUE =
+      new Function<TagLong, TagValue>() {
         @Override
-        public Object apply(TagLong tag) {
+        public TagValue apply(TagLong tag) {
           return tag.getValue();
         }
       };
 
-  private static final Function<TagBoolean, Object> GET_BOOLEAN_TAG_VALUE =
-      new Function<TagBoolean, Object>() {
+  private static final Function<TagBoolean, TagValue> GET_BOOLEAN_TAG_VALUE =
+      new Function<TagBoolean, TagValue>() {
         @Override
-        public Object apply(TagBoolean tag) {
+        public TagValue apply(TagBoolean tag) {
           return tag.getValue();
         }
       };
 
   // TODO(sebright): Change this field to type TagValue once we have a TagValue class.
   @VisibleForTesting
-  static final Object UNKNOWN_TAG_VALUE = null;
+  static final TagValue UNKNOWN_TAG_VALUE = null;
 
   private final View view;
-  private final Map<List<Object>, List<MutableAggregation>> tagValueAggregationMap =
+  private final Map<List<TagValue>, List<MutableAggregation>> tagValueAggregationMap =
       Maps.newHashMap();
   @Nullable private final Timestamp start;
 
@@ -141,7 +142,7 @@ final class MutableViewData {
    * Record double stats with the given tags.
    */
   void record(TagContext context, double value) {
-    List<Object> tagValues = getTagValues(getTagMap(context), view.getColumns());
+    List<TagValue> tagValues = getTagValues(getTagMap(context), view.getColumns());
     if (!tagValueAggregationMap.containsKey(tagValues)) {
       List<MutableAggregation> aggregations = Lists.newArrayList();
       for (Aggregation aggregation : view.getAggregations()) {
@@ -162,11 +163,11 @@ final class MutableViewData {
     throw new UnsupportedOperationException("Not implemented.");
   }
 
-  private static Map<TagKey, Object> getTagMap(TagContext ctx) {
+  private static Map<TagKey, TagValue> getTagMap(TagContext ctx) {
     if (ctx instanceof TagContextImpl) {
       return ((TagContextImpl) ctx).getTags();
     } else {
-      Map<TagKey, Object> tags = Maps.newHashMap();
+      Map<TagKey, TagValue> tags = Maps.newHashMap();
       for (Iterator<Tag> i = ctx.unsafeGetIterator(); i.hasNext(); ) {
         Tag tag = i.next();
         tags.put(
@@ -175,7 +176,7 @@ final class MutableViewData {
                 GET_STRING_TAG_VALUE,
                 GET_LONG_TAG_VALUE,
                 GET_BOOLEAN_TAG_VALUE,
-                Functions.throwAssertionError()));
+                Functions.<TagValue>throwAssertionError()));
       }
       return tags;
     }
@@ -185,8 +186,8 @@ final class MutableViewData {
    * Convert this {@link MutableViewData} to {@link ViewData}.
    */
   ViewData toViewData(Clock clock) {
-    Map<List<Object>, List<AggregationData>> map = Maps.newHashMap();
-    for (Entry<List<Object>, List<MutableAggregation>> entry :
+    Map<List<TagValue>, List<AggregationData>> map = Maps.newHashMap();
+    for (Entry<List<TagValue>, List<MutableAggregation>> entry :
         tagValueAggregationMap.entrySet()) {
       List<AggregationData> aggregates = Lists.newArrayList();
       for (MutableAggregation aggregation : entry.getValue()) {
@@ -206,9 +207,9 @@ final class MutableViewData {
   }
 
   @VisibleForTesting
-  static List<Object> getTagValues(
-      Map<? extends TagKey, ? extends Object> tags, List<? extends TagKey> columns) {
-    List<Object> tagValues = new ArrayList<Object>(columns.size());
+  static List<TagValue> getTagValues(
+      Map<? extends TagKey, ? extends TagValue> tags, List<? extends TagKey> columns) {
+    List<TagValue> tagValues = new ArrayList<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) {
diff --git a/core_impl/src/main/java/io/opencensus/implcore/tags/SerializationUtils.java b/core_impl/src/main/java/io/opencensus/implcore/tags/SerializationUtils.java
index 7b648f1e..d43cc5d3 100644
--- a/core_impl/src/main/java/io/opencensus/implcore/tags/SerializationUtils.java
+++ b/core_impl/src/main/java/io/opencensus/implcore/tags/SerializationUtils.java
@@ -28,7 +28,8 @@ import io.opencensus.tags.Tag.TagString;
 import io.opencensus.tags.TagContext;
 import io.opencensus.tags.TagKey;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue;
+import io.opencensus.tags.TagValue.TagValueString;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
@@ -137,7 +138,7 @@ final class SerializationUtils {
   static TagContextImpl deserializeBinary(InputStream input) throws IOException {
     try {
       byte[] bytes = ByteStreams.toByteArray(input);
-      HashMap<TagKey, Object> tags = new HashMap<TagKey, Object>();
+      HashMap<TagKey, TagValue> tags = new HashMap<TagKey, TagValue>();
       if (bytes.length == 0) {
         // Does not allow empty byte array.
         throw new IOException("Input byte stream can not be empty.");
diff --git a/core_impl/src/main/java/io/opencensus/implcore/tags/TagContextBuilderImpl.java b/core_impl/src/main/java/io/opencensus/implcore/tags/TagContextBuilderImpl.java
index f456fa3d..d22b1c49 100644
--- a/core_impl/src/main/java/io/opencensus/implcore/tags/TagContextBuilderImpl.java
+++ b/core_impl/src/main/java/io/opencensus/implcore/tags/TagContextBuilderImpl.java
@@ -23,19 +23,22 @@ import io.opencensus.tags.TagKey;
 import io.opencensus.tags.TagKey.TagKeyBoolean;
 import io.opencensus.tags.TagKey.TagKeyLong;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue;
+import io.opencensus.tags.TagValue.TagValueBoolean;
+import io.opencensus.tags.TagValue.TagValueLong;
+import io.opencensus.tags.TagValue.TagValueString;
 import java.util.HashMap;
 import java.util.Map;
 
 final class TagContextBuilderImpl extends TagContextBuilder {
-  private final Map<TagKey, Object> tags;
+  private final Map<TagKey, TagValue> tags;
 
-  TagContextBuilderImpl(Map<TagKey, Object> tags) {
-    this.tags = new HashMap<TagKey, Object>(tags);
+  TagContextBuilderImpl(Map<TagKey, TagValue> tags) {
+    this.tags = new HashMap<TagKey, TagValue>(tags);
   }
 
   TagContextBuilderImpl() {
-    this.tags = new HashMap<TagKey, Object>();
+    this.tags = new HashMap<TagKey, TagValue>();
   }
 
   @Override
@@ -44,16 +47,16 @@ final class TagContextBuilderImpl extends TagContextBuilder {
   }
 
   @Override
-  public TagContextBuilderImpl set(TagKeyLong key, long value) {
+  public TagContextBuilderImpl set(TagKeyLong key, TagValueLong value) {
     return setInternal(key, value);
   }
 
   @Override
-  public TagContextBuilderImpl set(TagKeyBoolean key, boolean value) {
+  public TagContextBuilderImpl set(TagKeyBoolean key, TagValueBoolean value) {
     return setInternal(key, value);
   }
 
-  private TagContextBuilderImpl setInternal(TagKey key, Object value) {
+  private TagContextBuilderImpl setInternal(TagKey key, TagValue value) {
     tags.put(checkNotNull(key), value);
     return this;
   }
diff --git a/core_impl/src/main/java/io/opencensus/implcore/tags/TagContextImpl.java b/core_impl/src/main/java/io/opencensus/implcore/tags/TagContextImpl.java
index 36a7383b..780b7c02 100644
--- a/core_impl/src/main/java/io/opencensus/implcore/tags/TagContextImpl.java
+++ b/core_impl/src/main/java/io/opencensus/implcore/tags/TagContextImpl.java
@@ -27,7 +27,10 @@ import io.opencensus.tags.TagKey;
 import io.opencensus.tags.TagKey.TagKeyBoolean;
 import io.opencensus.tags.TagKey.TagKeyLong;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue;
+import io.opencensus.tags.TagValue.TagValueBoolean;
+import io.opencensus.tags.TagValue.TagValueLong;
+import io.opencensus.tags.TagValue.TagValueString;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Iterator;
@@ -38,16 +41,16 @@ import javax.annotation.concurrent.Immutable;
 @Immutable
 public final class TagContextImpl extends TagContext {
 
-  static final TagContextImpl EMPTY = new TagContextImpl(Collections.<TagKey, Object>emptyMap());
+  static final TagContextImpl EMPTY = new TagContextImpl(Collections.<TagKey, TagValue>emptyMap());
 
   // The types of the TagKey and value must match for each entry.
-  private final Map<TagKey, Object> tags;
+  private final Map<TagKey, TagValue> tags;
 
-  TagContextImpl(Map<? extends TagKey, ?> tags) {
-    this.tags = Collections.unmodifiableMap(new HashMap<TagKey, Object>(tags));
+  TagContextImpl(Map<? extends TagKey, ? extends TagValue> tags) {
+    this.tags = Collections.unmodifiableMap(new HashMap<TagKey, TagValue>(tags));
   }
 
-  public Map<TagKey, Object> getTags() {
+  public Map<TagKey, TagValue> getTags() {
     return tags;
   }
 
@@ -57,9 +60,9 @@ public final class TagContextImpl extends TagContext {
   }
 
   private static final class TagIterator implements Iterator<Tag> {
-    Iterator<Map.Entry<TagKey, Object>> iterator;
+    Iterator<Map.Entry<TagKey, TagValue>> iterator;
 
-    TagIterator(Map<TagKey, Object> tags) {
+    TagIterator(Map<TagKey, TagValue> tags) {
       iterator = tags.entrySet().iterator();
     }
 
@@ -70,8 +73,8 @@ public final class TagContextImpl extends TagContext {
 
     @Override
     public Tag next() {
-      final Entry<TagKey, Object> next = iterator.next();
-      Object value = next.getValue();
+      final Entry<TagKey, TagValue> next = iterator.next();
+      TagValue value = next.getValue();
       return next.getKey()
           .match(
               new NewTagString(value),
@@ -86,9 +89,9 @@ public final class TagContextImpl extends TagContext {
     }
 
     private static class NewTagString implements Function<TagKeyString, Tag> {
-      private final Object value;
+      private final TagValue value;
 
-      NewTagString(Object value) {
+      NewTagString(TagValue value) {
         this.value = value;
       }
 
@@ -99,28 +102,28 @@ public final class TagContextImpl extends TagContext {
     }
 
     private static class NewTagLong implements Function<TagKeyLong, Tag> {
-      private final Object value;
+      private final TagValue value;
 
-      NewTagLong(Object value) {
+      NewTagLong(TagValue value) {
         this.value = value;
       }
 
       @Override
       public Tag apply(TagKeyLong key) {
-        return TagLong.create(key, (Long) value);
+        return TagLong.create(key, (TagValueLong) value);
       }
     }
 
     private static class NewTagBoolean implements Function<TagKeyBoolean, Tag> {
-      private final Object value;
+      private final TagValue value;
 
-      NewTagBoolean(Object value) {
+      NewTagBoolean(TagValue value) {
         this.value = value;
       }
 
       @Override
       public Tag apply(TagKeyBoolean key) {
-        return TagBoolean.create(key, (Boolean) value);
+        return TagBoolean.create(key, (TagValueBoolean) value);
       }
     }
   }
diff --git a/core_impl/src/test/java/io/opencensus/implcore/stats/MutableViewDataTest.java b/core_impl/src/test/java/io/opencensus/implcore/stats/MutableViewDataTest.java
index f6e7c318..d4259ccd 100644
--- a/core_impl/src/test/java/io/opencensus/implcore/stats/MutableViewDataTest.java
+++ b/core_impl/src/test/java/io/opencensus/implcore/stats/MutableViewDataTest.java
@@ -38,7 +38,7 @@ import io.opencensus.stats.AggregationData.SumData;
 import io.opencensus.stats.BucketBoundaries;
 import io.opencensus.stats.UnreleasedApiAccessor;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue.TagValueString;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
diff --git a/core_impl/src/test/java/io/opencensus/implcore/stats/StatsTestUtil.java b/core_impl/src/test/java/io/opencensus/implcore/stats/StatsTestUtil.java
index 14bdaa5e..1ce8dc18 100644
--- a/core_impl/src/test/java/io/opencensus/implcore/stats/StatsTestUtil.java
+++ b/core_impl/src/test/java/io/opencensus/implcore/stats/StatsTestUtil.java
@@ -29,6 +29,7 @@ import io.opencensus.stats.AggregationData.MeanData;
 import io.opencensus.stats.AggregationData.RangeData;
 import io.opencensus.stats.AggregationData.StdDevData;
 import io.opencensus.stats.AggregationData.SumData;
+import io.opencensus.tags.TagValue;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
@@ -68,11 +69,11 @@ final class StatsTestUtil {
    * @param tolerance the tolerance used for {@code double} comparison.
    */
   static void assertAggregationMapEquals(
-      Map<? extends List<? extends Object>, List<AggregationData>> actual,
-      Map<? extends List<? extends Object>, List<AggregationData>> expected,
+      Map<? extends List<? extends TagValue>, List<AggregationData>> actual,
+      Map<? extends List<? extends TagValue>, List<AggregationData>> expected,
       double tolerance) {
     assertThat(actual.keySet()).containsExactlyElementsIn(expected.keySet());
-    for (List<? extends Object> tagValues : actual.keySet()) {
+    for (List<? extends TagValue> tagValues : actual.keySet()) {
       assertAggregationDataListEquals(expected.get(tagValues), actual.get(tagValues), tolerance);
     }
   }
diff --git a/core_impl/src/test/java/io/opencensus/implcore/stats/ViewManagerImplTest.java b/core_impl/src/test/java/io/opencensus/implcore/stats/ViewManagerImplTest.java
index 52b445ca..d38f0597 100644
--- a/core_impl/src/test/java/io/opencensus/implcore/stats/ViewManagerImplTest.java
+++ b/core_impl/src/test/java/io/opencensus/implcore/stats/ViewManagerImplTest.java
@@ -43,7 +43,7 @@ import io.opencensus.stats.ViewData.WindowData.CumulativeData;
 import io.opencensus.tags.TagContext;
 import io.opencensus.tags.TagContexts;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue.TagValueString;
 import io.opencensus.testing.common.TestClock;
 import java.util.Arrays;
 import java.util.Collections;
diff --git a/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextDeserializationTest.java b/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextDeserializationTest.java
index 5b43f5e1..e9da5c87 100644
--- a/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextDeserializationTest.java
+++ b/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextDeserializationTest.java
@@ -24,7 +24,7 @@ import io.opencensus.tags.TagContext;
 import io.opencensus.tags.TagContextBinarySerializer;
 import io.opencensus.tags.TagContexts;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue.TagValueString;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
diff --git a/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextImplTest.java b/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextImplTest.java
index 3afefd00..f609a393 100644
--- a/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextImplTest.java
+++ b/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextImplTest.java
@@ -30,7 +30,9 @@ import io.opencensus.tags.TagContexts;
 import io.opencensus.tags.TagKey.TagKeyBoolean;
 import io.opencensus.tags.TagKey.TagKeyLong;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue.TagValueBoolean;
+import io.opencensus.tags.TagValue.TagValueLong;
+import io.opencensus.tags.TagValue.TagValueString;
 import io.opencensus.tags.UnreleasedApiAccessor;
 import java.util.Arrays;
 import java.util.Iterator;
@@ -66,13 +68,13 @@ public class TagContextImplTest {
                 tagContexts
                     .emptyBuilder()
                     .set(stringKey, TagValueString.create("value"))
-                    .set(longKey, 123)
-                    .set(boolKey, true)
+                    .set(longKey, TagValueLong.create(123))
+                    .set(boolKey, TagValueBoolean.create(true))
                     .build()))
         .containsExactly(
             TagString.create(stringKey, TagValueString.create("value")),
-            TagLong.create(longKey, 123L),
-            TagBoolean.create(boolKey, true));
+            TagLong.create(longKey, TagValueLong.create(123L)),
+            TagBoolean.create(boolKey, TagValueBoolean.create(true)));
   }
 
   @Test
diff --git a/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextRoundtripTest.java b/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextRoundtripTest.java
index 4f9b8622..e8a6dfde 100644
--- a/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextRoundtripTest.java
+++ b/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextRoundtripTest.java
@@ -23,7 +23,7 @@ import io.opencensus.tags.TagContext;
 import io.opencensus.tags.TagContextBinarySerializer;
 import io.opencensus.tags.TagContexts;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue.TagValueString;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import org.junit.Test;
diff --git a/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextSerializationTest.java b/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextSerializationTest.java
index 25b4ca35..f21c40af 100644
--- a/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextSerializationTest.java
+++ b/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextSerializationTest.java
@@ -25,7 +25,7 @@ import io.opencensus.tags.TagContextBinarySerializer;
 import io.opencensus.tags.TagContextBuilder;
 import io.opencensus.tags.TagContexts;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue.TagValueString;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.util.Arrays;
diff --git a/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextsImplTest.java b/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextsImplTest.java
index 1924264f..fb78287e 100644
--- a/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextsImplTest.java
+++ b/core_impl/src/test/java/io/opencensus/implcore/tags/TagContextsImplTest.java
@@ -28,7 +28,9 @@ import io.opencensus.tags.TagContexts;
 import io.opencensus.tags.TagKey.TagKeyBoolean;
 import io.opencensus.tags.TagKey.TagKeyLong;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue.TagValueBoolean;
+import io.opencensus.tags.TagValue.TagValueLong;
+import io.opencensus.tags.TagValue.TagValueString;
 import io.opencensus.tags.UnreleasedApiAccessor;
 import java.util.Collections;
 import java.util.Iterator;
@@ -48,8 +50,10 @@ public class TagContextsImplTest {
   private static final TagKeyLong KL = UnreleasedApiAccessor.createTagKeyLong("kl");
   private static final TagKeyBoolean KB = UnreleasedApiAccessor.createTagKeyBoolean("kb");
 
-  private static final TagValueString V1 = TagValueString.create("v1");
-  private static final TagValueString V2 = TagValueString.create("v2");
+  private static final TagValueString VS1 = TagValueString.create("v1");
+  private static final TagValueString VS2 = TagValueString.create("v2");
+  private static final TagValueLong VL = TagValueLong.create(10L);
+  private static final TagValueBoolean VB = TagValueBoolean.create(false);
 
   @Rule public final ExpectedException thrown = ExpectedException.none();
 
@@ -65,9 +69,9 @@ public class TagContextsImplTest {
 
   @Test
   public void toBuilder_ConvertUnknownTagContextToTagContextImpl() {
-    Tag tag1 = TagString.create(KS, V1);
-    Tag tag2 = TagLong.create(KL, 10L);
-    Tag tag3 = TagBoolean.create(KB, false);
+    Tag tag1 = TagString.create(KS, VS1);
+    Tag tag2 = TagLong.create(KL, VL);
+    Tag tag3 = TagBoolean.create(KB, VB);
     TagContext unknownTagContext = new SimpleTagContext(tag1, tag2, tag3);
     TagContext newTagContext = tagContexts.toBuilder(unknownTagContext).build();
     assertThat(asList(newTagContext)).containsExactly(tag1, tag2, tag3);
@@ -76,8 +80,8 @@ public class TagContextsImplTest {
 
   @Test
   public void toBuilder_RemoveDuplicatesFromUnknownTagContext() {
-    Tag tag1 = TagString.create(KS, V1);
-    Tag tag2 = TagString.create(KS, V2);
+    Tag tag1 = TagString.create(KS, VS1);
+    Tag tag2 = TagString.create(KS, VS2);
     TagContext unknownTagContext = new SimpleTagContext(tag1, tag2);
     TagContext newTagContext = tagContexts.toBuilder(unknownTagContext).build();
     assertThat(asList(newTagContext)).containsExactly(tag2);
@@ -86,7 +90,7 @@ public class TagContextsImplTest {
   @Test
   public void toBuilder_HandleNullTag() {
     TagContext unknownTagContext =
-        new SimpleTagContext(TagString.create(KS, V2), null, TagLong.create(KL, 5L));
+        new SimpleTagContext(TagString.create(KS, VS2), null, TagLong.create(KL, VL));
     thrown.expect(NullPointerException.class);
     tagContexts.toBuilder(unknownTagContext).build();
   }
diff --git a/examples/src/main/java/io/opencensus/examples/stats/StatsRunner.java b/examples/src/main/java/io/opencensus/examples/stats/StatsRunner.java
index 1301af00..95fff962 100644
--- a/examples/src/main/java/io/opencensus/examples/stats/StatsRunner.java
+++ b/examples/src/main/java/io/opencensus/examples/stats/StatsRunner.java
@@ -24,7 +24,7 @@ import io.opencensus.stats.StatsRecorder;
 import io.opencensus.tags.TagContext;
 import io.opencensus.tags.TagContexts;
 import io.opencensus.tags.TagKey.TagKeyString;
-import io.opencensus.tags.TagValueString;
+import io.opencensus.tags.TagValue.TagValueString;
 import io.opencensus.tags.Tags;
 
 /** Simple program that uses Stats contexts. */