fixed issue 46 by adding toString() methods to Gson, serializers, deserializers, and instanceCreators, and default type adapters.

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

@@ -191,6 +191,14 @@ final class DefaultTypeAdapters {
         throw new JsonParseException(e);
       }
     }
+    
+    @Override
+    public String toString() {
+      StringBuilder sb = new StringBuilder();
+      sb.append(DefaultDateTypeAdapter.class.getSimpleName());
+      sb.append('(').append(format.getClass().getSimpleName()).append(')');
+      return sb.toString();
+    }
   }
 
   @SuppressWarnings("unchecked")
@@ -218,6 +226,10 @@ final class DefaultTypeAdapters {
         throw new RuntimeException(e);
       }
     }
+    @Override
+    public String toString() {
+      return EnumTypeAdapter.class.getSimpleName();
+    }
   }
 
   private static class UrlTypeAdapter implements JsonSerializer<URL>, JsonDeserializer<URL>,
@@ -240,6 +252,10 @@ final class DefaultTypeAdapters {
         throw new RuntimeException(e);
       }
     }
+    @Override
+    public String toString() {
+      return UrlTypeAdapter.class.getSimpleName();
+    }    
   }
 
   private static class UriTypeAdapter implements JsonSerializer<URI>, JsonDeserializer<URI> {
@@ -254,6 +270,10 @@ final class DefaultTypeAdapters {
         throw new JsonParseException(e);
       }
     }
+    @Override
+    public String toString() {
+      return UriTypeAdapter.class.getSimpleName();
+    }
   }
 
   private static class LocaleTypeAdapter implements JsonSerializer<Locale>,
@@ -288,6 +308,10 @@ final class DefaultTypeAdapters {
     public Locale createInstance(Type type) {
       return new Locale("en_US");
     }
+    @Override
+    public String toString() {
+      return LocaleTypeAdapter.class.getSimpleName();
+    }
   }
 
   @SuppressWarnings("unchecked")
@@ -317,6 +341,10 @@ final class DefaultTypeAdapters {
     public Map createInstance(Type type) {
       return new LinkedHashMap();
     }
+    @Override
+    public String toString() {
+      return MapTypeAdapter.class.getSimpleName();
+    }
   }
 
   private static class BigDecimalTypeAdapter implements JsonSerializer<BigDecimal>,
@@ -334,6 +362,10 @@ final class DefaultTypeAdapters {
     public BigDecimal createInstance(Type type) {
       return new BigDecimal(0);
     }
+    @Override
+    public String toString() {
+      return BigDecimalTypeAdapter.class.getSimpleName();
+    }
   }
 
   private static class BigIntegerTypeAdapter implements JsonSerializer<BigInteger>,
@@ -351,65 +383,109 @@ final class DefaultTypeAdapters {
     public BigInteger createInstance(Type type) {
       return new BigInteger("0");
     }
+    @Override
+    public String toString() {
+      return BigIntegerTypeAdapter.class.getSimpleName();
+    }
   }
 
   private static class LongCreator implements InstanceCreator<Long> {
     public Long createInstance(Type type) {
       return new Long(0L);
     }
+    @Override
+    public String toString() {
+      return LongCreator.class.getSimpleName();
+    }
   }
 
   private static class IntegerCreator implements InstanceCreator<Integer> {
     public Integer createInstance(Type type) {
       return new Integer(0);
     }
+    @Override
+    public String toString() {
+      return IntegerCreator.class.getSimpleName();
+    }
   }
 
   private static class ShortCreator implements InstanceCreator<Short> {
     public Short createInstance(Type type) {
       return new Short((short) 0);
     }
+    @Override
+    public String toString() {
+      return ShortCreator.class.getSimpleName();
+    }
   }
 
   private static class ByteCreator implements InstanceCreator<Byte> {
     public Byte createInstance(Type type) {
       return new Byte((byte) 0);
     }
+    @Override
+    public String toString() {
+      return ByteCreator.class.getSimpleName();
+    }
   }
 
   private static class FloatCreator implements InstanceCreator<Float> {
     public Float createInstance(Type type) {
       return new Float(0F);
     }
+    @Override
+    public String toString() {
+      return FloatCreator.class.getSimpleName();
+    }
   }
 
   private static class DoubleCreator implements InstanceCreator<Double> {
     public Double createInstance(Type type) {
       return new Double(0D);
     }
+    @Override
+    public String toString() {
+      return DoubleCreator.class.getSimpleName();
+    }
   }
 
   private static class CharacterCreator implements InstanceCreator<Character> {
     public Character createInstance(Type type) {
       return new Character((char) 0);
     }
+    @Override
+    public String toString() {
+      return CharacterCreator.class.getSimpleName();
+    }
   }
 
   private static class BooleanCreator implements InstanceCreator<Boolean> {
     public Boolean createInstance(Type type) {
       return new Boolean(false);
     }
+    @Override
+    public String toString() {
+      return BooleanCreator.class.getSimpleName();
+    }
   }
 
   private static class LinkedListCreator implements InstanceCreator<LinkedList<?>> {
     public LinkedList<?> createInstance(Type type) {
       return new LinkedList<Object>();
     }
+    @Override
+    public String toString() {
+      return LinkedListCreator.class.getSimpleName();
+    }
   }
 
   private static class TreeSetCreator implements InstanceCreator<TreeSet<?>> {
     public TreeSet<?> createInstance(Type type) {
       return new TreeSet<Object>();
     }
+    @Override
+    public String toString() {
+      return TreeSetCreator.class.getSimpleName();
+    }
   }
 }

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

@@ -401,4 +401,18 @@ public final class Gson {
       throw new JsonParseException(e);
     }
   }
+  
+  @Override 
+  public String toString() {
+	StringBuilder sb = new StringBuilder("{");
+    sb.append("serializeNulls:").append(serializeNulls);
+	sb.append(",serializers:").append(serializers);
+	sb.append(",deserializers:").append(deserializers);
+	// using the name instanceCreator instead of ObjectConstructor since the users of Gson are 
+	// more familiar with the concept of Instance Creators. Moreover, the objectConstructor is
+	// just a utility class around instance creators, and its toString() only displays them.
+    sb.append(",instanceCreators:").append(objectConstructor);
+	sb.append("}");
+	return sb.toString();
+  }
 }

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

@@ -63,4 +63,9 @@ class JsonDeserializerExceptionWrapper<T> implements JsonDeserializer<T> {
       throw new JsonParseException(errorMsg.toString(), e);
     }
   }
+  
+  @Override
+  public String toString() {
+    return delegate.toString();
+  }
 }

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

@@ -61,4 +61,9 @@ class JsonSerializerExceptionWrapper<T> implements JsonSerializer<T> {
       throw new JsonParseException(errorMsg.toString(), e);
     }
   }
+  
+  @Override
+  public String toString() {
+    return delegate.toString();
+  }
 }

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

@@ -21,6 +21,7 @@ import java.lang.reflect.Array;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Type;
+import java.util.Map;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
@@ -106,4 +107,9 @@ final class MappedObjectConstructor implements ObjectConstructor {
     }
     instanceCreatorMap.register(typeOfT, creator);
   }
+  
+  @Override
+  public String toString() {
+    return instanceCreatorMap.toString();
+  }
 }

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

@@ -90,4 +90,24 @@ final class ParameterizedTypeHandlerMap<T> {
   public synchronized Set<Map.Entry<Type, T>> entrySet() {
     return map.entrySet();
   }
+  
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder("{");
+    boolean first = true;
+    for (Map.Entry<Type, T> entry : map.entrySet()) {
+      if (first) {
+        first = false;
+      } else {
+        sb.append(',');
+      }
+      sb.append(typeToString(entry.getKey())).append(':');
+      sb.append(entry.getValue());
+    }
+    return sb.toString();
+  }
+  
+  private String typeToString(Type type) {
+    return TypeUtils.toRawClass(type).getSimpleName();
+  }
 }