Lower "expected degree" for internal maps, of which we have O(N) per …

…graph/network. This greatly reduces memory consumption for graphs of small average degree, in exchange for a small performance hit for graphs of large average degree.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=125369630

guava/src/com/google/common/graph/AbstractConfigurableGraph.java

@@ -18,6 +18,7 @@
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.graph.GraphConstants.DEFAULT_NODE_COUNT;
 import static com.google.common.graph.GraphErrorMessageUtils.NODE_NOT_IN_GRAPH;
 
 import com.google.common.collect.Maps;
@@ -53,9 +54,6 @@
  * @param <N> Node parameter type
  */
 abstract class AbstractConfigurableGraph<N> extends AbstractGraph<N> {
-  // The default of 11 is rather arbitrary, but roughly matches the sizing of just new HashMap()
-  private static final int DEFAULT_MAP_SIZE = 11;
-
   private final boolean isDirected;
   private final boolean allowsSelfLoops;
   private final ElementOrder<? super N> nodeOrder;
@@ -71,7 +69,7 @@ abstract class AbstractConfigurableGraph<N> extends AbstractGraph<N> {
 
   private static <S> Map<S, NodeAdjacencies<S>> getNodeMapforBuilder(
       GraphBuilder<? super S> builder) {
-    int expectedNodeSize = builder.expectedNodeCount.or(DEFAULT_MAP_SIZE);
+    int expectedNodeSize = builder.expectedNodeCount.or(DEFAULT_NODE_COUNT);
     switch (builder.nodeOrder.type()) {
         case UNORDERED:
           return Maps.newHashMapWithExpectedSize(expectedNodeSize);

guava/src/com/google/common/graph/AbstractConfigurableNetwork.java

@@ -18,6 +18,8 @@
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.graph.GraphConstants.DEFAULT_EDGE_COUNT;
+import static com.google.common.graph.GraphConstants.DEFAULT_NODE_COUNT;
 import static com.google.common.graph.GraphErrorMessageUtils.EDGE_NOT_IN_GRAPH;
 import static com.google.common.graph.GraphErrorMessageUtils.NODE_NOT_IN_GRAPH;
 
@@ -59,9 +61,6 @@
  * @param <E> Edge parameter type
  */
 abstract class AbstractConfigurableNetwork<N, E> extends AbstractNetwork<N, E> {
-  // The default of 11 is rather arbitrary, but roughly matches the sizing of just new HashMap()
-  private static final int DEFAULT_MAP_SIZE = 11;
-
   private final boolean isDirected;
   private final boolean allowsParallelEdges;
   private final boolean allowsSelfLoops;
@@ -86,7 +85,7 @@ abstract class AbstractConfigurableNetwork<N, E> extends AbstractNetwork<N, E> {
 
   private static <S, T> Map<S, NodeConnections<S, T>> getNodeMapForBuilder(
       NetworkBuilder<? super S, ? super T> builder) {
-    int expectedNodeSize = builder.expectedNodeCount.or(DEFAULT_MAP_SIZE);
+    int expectedNodeSize = builder.expectedNodeCount.or(DEFAULT_NODE_COUNT);
     switch (builder.nodeOrder.type()) {
         case UNORDERED:
           return Maps.newHashMapWithExpectedSize(expectedNodeSize);
@@ -101,7 +100,7 @@ private static <S, T> Map<S, NodeConnections<S, T>> getNodeMapForBuilder(
 
   private static <S, T> Map<T, S> getEdgeMapForBuilder(
       NetworkBuilder<? super S, ? super T> builder) {
-    int expectedEdgeSize = builder.expectedEdgeCount.or(DEFAULT_MAP_SIZE);
+    int expectedEdgeSize = builder.expectedEdgeCount.or(DEFAULT_EDGE_COUNT);
     switch (builder.edgeOrder.type()) {
         case UNORDERED:
           return Maps.newHashMapWithExpectedSize(expectedEdgeSize);

guava/src/com/google/common/graph/DirectedNodeAdjacencies.java

@@ -59,8 +59,10 @@ private DirectedNodeAdjacencies(
   }
 
   static <N> DirectedNodeAdjacencies<N> of() {
+    // We store predecessors and successors in the same map, so expected size is twice the degree.
+    int inAndOutDegree = EXPECTED_DEGREE * 2;
     return new DirectedNodeAdjacencies<N>(
-        Maps.<N, Adjacency>newHashMapWithExpectedSize(EXPECTED_DEGREE), 0, 0);
+        Maps.<N, Adjacency>newHashMapWithExpectedSize(inAndOutDegree), 0, 0);
   }
 
   static <N> DirectedNodeAdjacencies<N> ofImmutable(

guava/src/com/google/common/graph/GraphConstants.java

@@ -19,11 +19,14 @@
 /**
  * A utility class to hold various constants used by the Guava Graph library.
  */
-// TODO(user): Decide what else to put here (error message strings, node/edge map sizes, etc.)
+// TODO(user): Decide what else to put here (error message strings, etc.)
 final class GraphConstants {
 
   private GraphConstants() {}
 
-  // TODO(user): Enable users to specify the expected (in/out?) degree of nodes.
-  static final int EXPECTED_DEGREE = 11;
+  // TODO(user): Enable users to specify the expected degree of nodes.
+  static final int EXPECTED_DEGREE = 2;
+
+  static final int DEFAULT_NODE_COUNT = 10;
+  static final int DEFAULT_EDGE_COUNT = DEFAULT_NODE_COUNT * EXPECTED_DEGREE;
 }