Fixed Issue 54 to enable serialization of fields that are declared of type

Object.

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

@@ -124,6 +124,16 @@ final class JsonSerializationVisitor implements ObjectNavigator.Visitor {
       }
     } else {
       Object fieldValue = getFieldValue(f, obj);
+      // See if the fieldValue has better type information than the specified typeOfF
+      // This takes care of situations where the field was declared as an Object, but the
+      // actual value contains something more specific. See Issue 54.
+      if (fieldValue != null && typeOfF instanceof Class) {
+        Class<?> classOfF = (Class<?>) typeOfF;
+        Class<?> actualClassOfF = fieldValue.getClass();
+        if (classOfF.isAssignableFrom(actualClassOfF)) {
+          typeOfF = actualClassOfF;
+        }
+      }
       addAsChildOfObject(f, typeOfF, fieldValue);
     }
   }

gson/src/test/java/com/google/gson/functional/ObjectTest.java

@@ -361,6 +361,21 @@ public class ObjectTest extends TestCase {
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
+  /**
+   * Tests that a class field with type Object can be serialized properly. 
+   * See issue 54
+   */
+  public void testClassWithObjectFieldSerialization() {
+    ClassWithObjectField obj = new ClassWithObjectField();
+    obj.member = "abc";
+    String json = gson.toJson(obj);
+    assertTrue(json.contains("abc"));
+  }
+  
+  private static class ClassWithObjectField {
+    Object member;
+  }
+  
   public void testInnerClassSerialization() {    
     Parent p = new Parent();
     Parent.Child c = p.new Child();
@@ -371,7 +386,8 @@ public class ObjectTest extends TestCase {
    
   public void testInnerClassDeserialization() {
     final Parent p = new Parent();
-    Gson gson = new GsonBuilder().registerTypeAdapter(Parent.Child.class, new InstanceCreator<Parent.Child>() {
+    Gson gson = new GsonBuilder().registerTypeAdapter(
+        Parent.Child.class, new InstanceCreator<Parent.Child>() {
       public Parent.Child createInstance(Type type) {
         return p.new Child();
       }