diff --git a/core/src/main/java/org/elasticsearch/search/aggregations/Aggregations.java b/core/src/main/java/org/elasticsearch/search/aggregations/Aggregations.java
index f7fe3e49f0a..ef84edfb729 100644
--- a/core/src/main/java/org/elasticsearch/search/aggregations/Aggregations.java
+++ b/core/src/main/java/org/elasticsearch/search/aggregations/Aggregations.java
@@ -18,31 +18,84 @@
  */
 package org.elasticsearch.search.aggregations;
 
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
+
+import static java.util.Collections.unmodifiableMap;
 
 /**
- * Represents a set of computed addAggregation.
+ * Represents a set of {@link Aggregation}s
  */
-public interface Aggregations extends Iterable<Aggregation> {
+public abstract class Aggregations implements Iterable<Aggregation> {
+
+    protected List<? extends Aggregation> aggregations = Collections.emptyList();
+    protected Map<String, Aggregation> aggregationsAsMap;
+
+    protected Aggregations() {
+    }
+
+    protected Aggregations(List<? extends Aggregation> aggregations) {
+        this.aggregations = aggregations;
+    }
+
+    /**
+     * Iterates over the {@link Aggregation}s.
+     */
+    @Override
+    public final Iterator<Aggregation> iterator() {
+        return aggregations.stream().map((p) -> (Aggregation) p).iterator();
+    }
 
     /**
      * The list of {@link Aggregation}s.
      */
-    List<Aggregation> asList();
+    public final List<Aggregation> asList() {
+        return Collections.unmodifiableList(aggregations);
+    }
 
     /**
      * Returns the {@link Aggregation}s keyed by aggregation name.
      */
-    Map<String, Aggregation> asMap();
+    public final Map<String, Aggregation> asMap() {
+        return getAsMap();
+    }
 
     /**
      * Returns the {@link Aggregation}s keyed by aggregation name.
      */
-    Map<String, Aggregation> getAsMap();
+    public final Map<String, Aggregation> getAsMap() {
+        if (aggregationsAsMap == null) {
+            Map<String, Aggregation> newAggregationsAsMap = new HashMap<>(aggregations.size());
+            for (Aggregation aggregation : aggregations) {
+                newAggregationsAsMap.put(aggregation.getName(), aggregation);
+            }
+            this.aggregationsAsMap = unmodifiableMap(newAggregationsAsMap);
+        }
+        return aggregationsAsMap;
+    }
 
     /**
      * Returns the aggregation that is associated with the specified name.
      */
-    <A extends Aggregation> A get(String name);
+    @SuppressWarnings("unchecked")
+    public final <A extends Aggregation> A get(String name) {
+        return (A) asMap().get(name);
+    }
+
+    @Override
+    public final boolean equals(Object obj) {
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+        return aggregations.equals(((Aggregations) obj).aggregations);
+    }
+
+    @Override
+    public final int hashCode() {
+        return Objects.hash(getClass(), aggregations);
+    }
 }
diff --git a/core/src/main/java/org/elasticsearch/search/aggregations/InternalAggregations.java b/core/src/main/java/org/elasticsearch/search/aggregations/InternalAggregations.java
index c835c47c148..64c9e4794c3 100644
--- a/core/src/main/java/org/elasticsearch/search/aggregations/InternalAggregations.java
+++ b/core/src/main/java/org/elasticsearch/search/aggregations/InternalAggregations.java
@@ -27,27 +27,18 @@ import org.elasticsearch.search.aggregations.InternalAggregation.ReduceContext;
 
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashMap;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
-import java.util.Objects;
-import java.util.stream.Collectors;
 
 import static java.util.Collections.emptyMap;
-import static java.util.Collections.unmodifiableMap;
 /**
  * An internal implementation of {@link Aggregations}.
  */
-public class InternalAggregations implements Aggregations, ToXContent, Streamable {
+public final class InternalAggregations extends Aggregations implements ToXContent, Streamable {
 
     public static final InternalAggregations EMPTY = new InternalAggregations();
 
-    private List<InternalAggregation> aggregations = Collections.emptyList();
-
-    private Map<String, Aggregation> aggregationsAsMap;
-
     private InternalAggregations() {
     }
 
@@ -55,55 +46,7 @@ public class InternalAggregations implements Aggregations, ToXContent, Streamabl
      * Constructs a new addAggregation.
      */
     public InternalAggregations(List<InternalAggregation> aggregations) {
-        this.aggregations = aggregations;
-    }
-
-    /**
-     * Iterates over the {@link Aggregation}s.
-     */
-    @Override
-    public Iterator<Aggregation> iterator() {
-        return aggregations.stream().map((p) -> (Aggregation) p).iterator();
-    }
-
-    /**
-     * The list of {@link Aggregation}s.
-     */
-    @Override
-    public List<Aggregation> asList() {
-        return aggregations.stream().map((p) -> (Aggregation) p).collect(Collectors.toList());
-    }
-
-    /**
-     * Returns the {@link Aggregation}s keyed by map.
-     */
-    @Override
-    public Map<String, Aggregation> asMap() {
-        return getAsMap();
-    }
-
-    /**
-     * Returns the {@link Aggregation}s keyed by map.
-     */
-    @Override
-    public Map<String, Aggregation> getAsMap() {
-        if (aggregationsAsMap == null) {
-            Map<String, InternalAggregation> newAggregationsAsMap = new HashMap<>();
-            for (InternalAggregation aggregation : aggregations) {
-                newAggregationsAsMap.put(aggregation.getName(), aggregation);
-            }
-            this.aggregationsAsMap = unmodifiableMap(newAggregationsAsMap);
-        }
-        return aggregationsAsMap;
-    }
-
-    /**
-     * @return the aggregation of the specified name.
-     */
-    @SuppressWarnings("unchecked")
-    @Override
-    public <A extends Aggregation> A get(String name) {
-        return (A) asMap().get(name);
+        super(aggregations);
     }
 
     /**
@@ -118,21 +61,16 @@ public class InternalAggregations implements Aggregations, ToXContent, Streamabl
         }
 
         // first we collect all aggregations of the same type and list them together
-
         Map<String, List<InternalAggregation>> aggByName = new HashMap<>();
         for (InternalAggregations aggregations : aggregationsList) {
-            for (InternalAggregation aggregation : aggregations.aggregations) {
-                List<InternalAggregation> aggs = aggByName.get(aggregation.getName());
-                if (aggs == null) {
-                    aggs = new ArrayList<>(aggregationsList.size());
-                    aggByName.put(aggregation.getName(), aggs);
-                }
-                aggs.add(aggregation);
+            for (Aggregation aggregation : aggregations.aggregations) {
+                List<InternalAggregation> aggs = aggByName.computeIfAbsent(
+                        aggregation.getName(), k -> new ArrayList<>(aggregationsList.size()));
+                aggs.add((InternalAggregation)aggregation);
             }
         }
 
         // now we can use the first aggregation of each list to handle the reduce of its list
-
         List<InternalAggregation> reducedAggregations = new ArrayList<>();
         for (Map.Entry<String, List<InternalAggregation>> entry : aggByName.entrySet()) {
             List<InternalAggregation> aggregations = entry.getValue();
@@ -142,41 +80,33 @@ public class InternalAggregations implements Aggregations, ToXContent, Streamabl
         return new InternalAggregations(reducedAggregations);
     }
 
-    /** The fields required to write this addAggregation to xcontent */
-    static class Fields {
-        public static final String AGGREGATIONS = "aggregations";
-    }
-
     @Override
     public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
         if (aggregations.isEmpty()) {
             return builder;
         }
-        builder.startObject(Fields.AGGREGATIONS);
+        builder.startObject("aggregations");
         toXContentInternal(builder, params);
         return builder.endObject();
     }
 
     /**
-     * Directly write all the addAggregation without their bounding object. Used by sub-addAggregation (non top level addAggregation)
+     * Directly write all the aggregations without their bounding object. Used by sub-aggregations (non top level aggs)
      */
     public XContentBuilder toXContentInternal(XContentBuilder builder, Params params) throws IOException {
         for (Aggregation aggregation : aggregations) {
-            ((InternalAggregation) aggregation).toXContent(builder, params);
+            ((InternalAggregation)aggregation).toXContent(builder, params);
         }
         return builder;
     }
 
+
     public static InternalAggregations readAggregations(StreamInput in) throws IOException {
         InternalAggregations result = new InternalAggregations();
         result.readFrom(in);
         return result;
     }
 
-    public static InternalAggregations readOptionalAggregations(StreamInput in) throws IOException {
-        return in.readOptionalStreamable(InternalAggregations::new);
-    }
-
     @Override
     public void readFrom(StreamInput in) throws IOException {
         aggregations = in.readList(stream -> in.readNamedWriteable(InternalAggregation.class));
@@ -186,20 +116,8 @@ public class InternalAggregations implements Aggregations, ToXContent, Streamabl
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeNamedWriteableList(aggregations);
-    }
-
-    @Override
-    public boolean equals(Object obj) {
-        if (obj == null || getClass() != obj.getClass()) {
-            return false;
-        }
-        return aggregations.equals(((InternalAggregations) obj).aggregations);
-    }
-
-    @Override
-    public int hashCode() {
-        return Objects.hash(getClass(), aggregations);
+        out.writeNamedWriteableList((List<InternalAggregation>)aggregations);
     }
 }