Make Measurement an opaque interface in the API. (#216)

api/src/main/java/openconsensus/stats/Measurement.java

@@ -16,105 +16,12 @@
 
 package openconsensus.stats;
 
-import com.google.auto.value.AutoValue;
 import javax.annotation.concurrent.Immutable;
 
 /**
- * Immutable representation of a Measurement.
+ * Immutable representation of a {@code Measurement}.
  *
  * @since 0.1.0
  */
 @Immutable
-public abstract class Measurement {
-
-  /**
-   * Extracts the measured {@link Measure}.
-   *
-   * @return the {@link Measure} if this measurement.
-   * @since 0.1.0
-   */
-  public abstract Measure getMeasure();
-
-  /**
-   * Returns the double value for the {@link Measurement}.
-   *
-   * <p>This method should only be called with {@link MeasurementDouble}.
-   *
-   * @return the double value.
-   * @throws UnsupportedOperationException if the {@code Measure} type is not {@link
-   *     Measure.Type#DOUBLE}.
-   * @since 0.1.0
-   */
-  public double getDoubleValue() {
-    throw new UnsupportedOperationException("This type can only return double data");
-  }
-
-  /**
-   * Returns the long value for the {@link Measurement}.
-   *
-   * <p>This method should only be called with {@link MeasurementLong}.
-   *
-   * @return the long value.
-   * @throws UnsupportedOperationException if the {@code Measure} type is not {@link
-   *     Measure.Type#LONG}.
-   * @since 0.1.0
-   */
-  public long getLongValue() {
-    throw new UnsupportedOperationException("This type can only return long data");
-  }
-
-  // Prevents this class from being subclassed anywhere else.
-  private Measurement() {}
-
-  /**
-   * {@code double} typed {@link Measurement}.
-   *
-   * @since 0.1.0
-   */
-  @Immutable
-  @AutoValue
-  public abstract static class MeasurementDouble extends Measurement {
-    MeasurementDouble() {}
-
-    /**
-     * Constructs a new {@link MeasurementDouble}.
-     *
-     * @since 0.1.0
-     */
-    public static MeasurementDouble create(Measure measure, double value) {
-      return new AutoValue_Measurement_MeasurementDouble(measure, value);
-    }
-
-    @Override
-    public abstract Measure getMeasure();
-
-    @Override
-    public abstract double getDoubleValue();
-  }
-
-  /**
-   * {@code long} typed {@link Measurement}.
-   *
-   * @since 0.1.0
-   */
-  @Immutable
-  @AutoValue
-  public abstract static class MeasurementLong extends Measurement {
-    MeasurementLong() {}
-
-    /**
-     * Constructs a new {@link MeasurementLong}.
-     *
-     * @since 0.1.0
-     */
-    public static MeasurementLong create(Measure measure, long value) {
-      return new AutoValue_Measurement_MeasurementLong(measure, value);
-    }
-
-    @Override
-    public abstract Measure getMeasure();
-
-    @Override
-    public abstract long getLongValue();
-  }
-}
+public interface Measurement {}

api/src/main/java/openconsensus/stats/NoopStats.java

@@ -21,8 +21,6 @@ import javax.annotation.concurrent.Immutable;
 import javax.annotation.concurrent.ThreadSafe;
 import openconsensus.internal.StringUtils;
 import openconsensus.internal.Utils;
-import openconsensus.stats.Measurement.MeasurementDouble;
-import openconsensus.stats.Measurement.MeasurementLong;
 import openconsensus.tags.TagMap;
 import openconsensus.trace.SpanContext;
 
@@ -89,21 +87,21 @@ public final class NoopStats {
     }
 
     @Override
-    public MeasurementDouble createDoubleMeasurement(double value) {
+    public Measurement createDoubleMeasurement(double value) {
       if (type != Type.DOUBLE) {
         throw new UnsupportedOperationException("This type can only create double measurement");
       }
       Utils.checkArgument(value >= 0.0, "Unsupported negative values.");
-      return MeasurementDouble.create(this, value);
+      return NoopMeasurement.INSTANCE;
     }
 
     @Override
-    public MeasurementLong createLongMeasurement(long value) {
+    public Measurement createLongMeasurement(long value) {
       if (type != Type.LONG) {
         throw new UnsupportedOperationException("This type can only create long measurement");
       }
       Utils.checkArgument(value >= 0, "Unsupported negative values.");
-      return MeasurementLong.create(this, value);
+      return NoopMeasurement.INSTANCE;
     }
 
     private static final class NoopBuilder implements Measure.Builder {
@@ -133,4 +131,9 @@ public final class NoopStats {
       }
     }
   }
+
+  @Immutable
+  private static final class NoopMeasurement implements Measurement {
+    private static final Measurement INSTANCE = new NoopMeasurement();
+  }
 }

sdk/src/main/java/openconsensus/sdk/stats/impl/MeasurementImpl.java

@@ -0,0 +1,115 @@
+/*
+ * Copyright 2019, OpenConsensus 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 openconsensus.sdk.stats.impl;
+
+import com.google.auto.value.AutoValue;
+import javax.annotation.concurrent.Immutable;
+import openconsensus.stats.Measure;
+import openconsensus.stats.Measurement;
+
+abstract class MeasurementImpl implements Measurement {
+  /**
+   * Extracts the measured {@link Measure}.
+   *
+   * @return the {@link Measure} if this measurement.
+   * @since 0.1.0
+   */
+  abstract Measure getMeasure();
+
+  /**
+   * Returns the double value for the {@link openconsensus.stats.Measurement}.
+   *
+   * <p>This method should only be called with {@link MeasurementDouble}.
+   *
+   * @return the double value.
+   * @throws UnsupportedOperationException if the {@code Measure} type is not {@link
+   *     Measure.Type#DOUBLE}.
+   * @since 0.1.0
+   */
+  double getDoubleValue() {
+    throw new UnsupportedOperationException("This type can only return double data");
+  }
+
+  /**
+   * Returns the long value for the {@link openconsensus.stats.Measurement}.
+   *
+   * <p>This method should only be called with {@link MeasurementLong}.
+   *
+   * @return the long value.
+   * @throws UnsupportedOperationException if the {@code Measure} type is not {@link
+   *     Measure.Type#LONG}.
+   * @since 0.1.0
+   */
+  long getLongValue() {
+    throw new UnsupportedOperationException("This type can only return long data");
+  }
+
+  // Prevents this class from being subclassed anywhere else.
+  private MeasurementImpl() {}
+
+  /**
+   * {@code double} typed {@link openconsensus.stats.Measurement}.
+   *
+   * @since 0.1.0
+   */
+  @Immutable
+  @AutoValue
+  abstract static class MeasurementDouble extends MeasurementImpl {
+    MeasurementDouble() {}
+
+    /**
+     * Constructs a new {@link MeasurementDouble}.
+     *
+     * @since 0.1.0
+     */
+    static MeasurementDouble create(Measure measure, double value) {
+      return new AutoValue_MeasurementImpl_MeasurementDouble(measure, value);
+    }
+
+    @Override
+    abstract Measure getMeasure();
+
+    @Override
+    abstract double getDoubleValue();
+  }
+
+  /**
+   * {@code long} typed {@link openconsensus.stats.Measurement}.
+   *
+   * @since 0.1.0
+   */
+  @Immutable
+  @AutoValue
+  abstract static class MeasurementLong extends MeasurementImpl {
+    MeasurementLong() {}
+
+    /**
+     * Constructs a new {@link MeasurementLong}.
+     *
+     * @since 0.1.0
+     */
+    static MeasurementLong create(Measure measure, long value) {
+      return new AutoValue_MeasurementImpl_MeasurementLong(measure, value);
+    }
+
+    @Override
+    abstract Measure getMeasure();
+
+    @Override
+    abstract long getLongValue();
+  }
+}