Pure refactorings:

Replaced DEFAULT_SERIALIZERS, DEFAULT_DESERIALIZERS and DEFAULT_INSTANCE_CREATORS with a single EMPTY_MAP.
Removed obsoleted TODO from Gson.
made ParameterizedTypeHandlerMap.makeUnmodifiable a builder method that returns this instance.

gson/src/main/java/com/google/gson/DefaultTypeAdapters.java

@@ -25,8 +25,6 @@ import java.util.Date;
 import java.util.Locale;
 import java.util.TimeZone;
 
-import com.google.gson.internal.ParameterizedTypeHandlerMap;
-
 /**
  * List of all the default type adapters ({@link JsonSerializer}s, {@link JsonDeserializer}s,
  * and {@link InstanceCreator}s.
@@ -35,38 +33,6 @@ import com.google.gson.internal.ParameterizedTypeHandlerMap;
  * @author Joel Leitch
  */
 final class DefaultTypeAdapters {
-
-  // The constants DEFAULT_SERIALIZERS, DEFAULT_DESERIALIZERS, and DEFAULT_INSTANCE_CREATORS
-  // must be defined after the constants for the type adapters. Otherwise, the type adapter
-  // constants will appear as nulls.
-  static final ParameterizedTypeHandlerMap<JsonSerializer<?>> DEFAULT_SERIALIZERS =
-      createDefaultSerializers();
-  static final ParameterizedTypeHandlerMap<JsonDeserializer<?>> DEFAULT_DESERIALIZERS =
-      createDefaultDeserializers();
-  static final ParameterizedTypeHandlerMap<InstanceCreator<?>> DEFAULT_INSTANCE_CREATORS =
-      createDefaultInstanceCreators();
-
-  private static ParameterizedTypeHandlerMap<JsonSerializer<?>> createDefaultSerializers() {
-    ParameterizedTypeHandlerMap<JsonSerializer<?>> map =
-        new ParameterizedTypeHandlerMap<JsonSerializer<?>>();
-    map.makeUnmodifiable();
-    return map;
-  }
-
-  private static ParameterizedTypeHandlerMap<JsonDeserializer<?>> createDefaultDeserializers() {
-    ParameterizedTypeHandlerMap<JsonDeserializer<?>> map =
-        new ParameterizedTypeHandlerMap<JsonDeserializer<?>>();
-    map.makeUnmodifiable();
-    return map;
-  }
-
-  private static ParameterizedTypeHandlerMap<InstanceCreator<?>> createDefaultInstanceCreators() {
-    ParameterizedTypeHandlerMap<InstanceCreator<?>> map
-        = new ParameterizedTypeHandlerMap<InstanceCreator<?>>();
-    map.makeUnmodifiable();
-    return map;
-  }
-
   /**
    * This type adapter supports three subclasses of date: Date, Timestamp, and
    * java.sql.Date.

gson/src/main/java/com/google/gson/Gson.java

@@ -99,9 +99,9 @@ import java.util.Map;
  * @author Joel Leitch
  */
 public final class Gson {
-
-  //TODO(inder): get rid of all the registerXXX methods and take all such parameters in the
-  // constructor instead. At the minimum, mark those methods private.
+  @SuppressWarnings("unchecked")
+  static final ParameterizedTypeHandlerMap EMPTY_MAP = 
+    new ParameterizedTypeHandlerMap().makeUnmodifiable();
 
    static final boolean DEFAULT_JSON_NON_EXECUTABLE = false;
 
@@ -170,11 +170,10 @@ public final class Gson {
    *   {@link GsonBuilder#excludeFieldsWithModifiers(int...)}.</li>
    * </ul>
    */
+  @SuppressWarnings("unchecked")
   public Gson() {
     this(DEFAULT_EXCLUSION_STRATEGY, DEFAULT_EXCLUSION_STRATEGY, DEFAULT_NAMING_POLICY,
-        DefaultTypeAdapters.DEFAULT_INSTANCE_CREATORS,
-        false, DefaultTypeAdapters.DEFAULT_SERIALIZERS,
-        DefaultTypeAdapters.DEFAULT_DESERIALIZERS, false, DEFAULT_JSON_NON_EXECUTABLE, true,
+        EMPTY_MAP, false, EMPTY_MAP, EMPTY_MAP, false, DEFAULT_JSON_NON_EXECUTABLE, true,
         false, false, LongSerializationPolicy.DEFAULT,
         Collections.<TypeAdapter.Factory>emptyList());
   }

gson/src/main/java/com/google/gson/GsonBuilder.java

@@ -677,24 +677,13 @@ public final class GsonBuilder {
       deserializationStrategies.add(exposeAnnotationDeserializationExclusionStrategy);
       serializationStrategies.add(exposeAnnotationSerializationExclusionStrategy);
     }
-
-    ParameterizedTypeHandlerMap<JsonSerializer<?>> customSerializers = serializers.copyOf();
-    ParameterizedTypeHandlerMap<JsonDeserializer<?>> customDeserializers = deserializers.copyOf();
-    addTypeAdaptersForDate(datePattern, dateStyle, timeStyle, customSerializers,
-        customDeserializers);
-
-    ParameterizedTypeHandlerMap<InstanceCreator<?>> customInstanceCreators =
-        instanceCreators.copyOf();
-
-    customSerializers.makeUnmodifiable();
-    customDeserializers.makeUnmodifiable();
-    customInstanceCreators.makeUnmodifiable();
+    addTypeAdaptersForDate(datePattern, dateStyle, timeStyle, serializers, deserializers);
 
     return new Gson(new DisjunctionExclusionStrategy(deserializationStrategies),
         new DisjunctionExclusionStrategy(serializationStrategies),
-        fieldNamingPolicy, customInstanceCreators, serializeNulls,
-        customSerializers, customDeserializers, complexMapKeySerialization,
-        generateNonExecutableJson, escapeHtmlChars, prettyPrinting,
+        fieldNamingPolicy, instanceCreators.copyOf().makeUnmodifiable(), serializeNulls,
+        serializers.copyOf().makeUnmodifiable(), deserializers.copyOf().makeUnmodifiable(),
+        complexMapKeySerialization, generateNonExecutableJson, escapeHtmlChars, prettyPrinting,
         serializeSpecialFloatingPointValues, longSerializationPolicy, typeAdapterFactories);
   }
 

gson/src/main/java/com/google/gson/internal/ParameterizedTypeHandlerMap.java

@@ -34,6 +34,7 @@ import java.util.logging.Logger;
  * @param <T> The handler that will be looked up by type
  */
 public final class ParameterizedTypeHandlerMap<T> {
+
   private static final Logger logger =
       Logger.getLogger(ParameterizedTypeHandlerMap.class.getName());
   /**
@@ -158,8 +159,9 @@ public final class ParameterizedTypeHandlerMap<T> {
     }
   }
 
-  public synchronized void makeUnmodifiable() {
+  public synchronized ParameterizedTypeHandlerMap<T> makeUnmodifiable() {
     modifiable = false;
+    return this;
   }
 
   public synchronized T getHandlerFor(Type type, boolean systemOnly) {

gson/src/test/java/com/google/gson/FunctionWithInternalDependenciesTest.java

@@ -33,15 +33,15 @@ import junit.framework.TestCase;
  */
 public class FunctionWithInternalDependenciesTest extends TestCase {
 
+  @SuppressWarnings("unchecked")
   public void testAnonymousLocalClassesSerialization() throws Exception {
     LinkedList<ExclusionStrategy> strategies = new LinkedList<ExclusionStrategy>();
     strategies.add(new SyntheticFieldExclusionStrategy(true));
     strategies.add(new ModifierBasedExclusionStrategy(Modifier.TRANSIENT, Modifier.STATIC));
     ExclusionStrategy exclusionStrategy = new DisjunctionExclusionStrategy(strategies);
     Gson gson = new Gson(exclusionStrategy, exclusionStrategy, Gson.DEFAULT_NAMING_POLICY,
-        DefaultTypeAdapters.DEFAULT_INSTANCE_CREATORS,
-        false, DefaultTypeAdapters.DEFAULT_SERIALIZERS,
-        DefaultTypeAdapters.DEFAULT_DESERIALIZERS, false, Gson.DEFAULT_JSON_NON_EXECUTABLE,
+        Gson.EMPTY_MAP, false, Gson.EMPTY_MAP, Gson.EMPTY_MAP, false,
+        Gson.DEFAULT_JSON_NON_EXECUTABLE,
         true, false, false, LongSerializationPolicy.DEFAULT,
         Collections.<TypeAdapter.Factory>emptyList());
     assertEquals("{}", gson.toJson(new ClassWithNoFields() {