Enable additional Error Prone checks & fix violations

extras/src/main/java/com/google/gson/extras/examples/rawcollections/RawCollectionsExample.java

@@ -21,6 +21,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 
+@SuppressWarnings({"PrivateConstructorForUtilityClass", "SystemOut"})
 public class RawCollectionsExample {
   static class Event {
     private String name;

extras/src/main/java/com/google/gson/typeadapters/PostConstructAdapterFactory.java

@@ -61,9 +61,11 @@ public T read(JsonReader in) throws IOException {
         try {
           method.invoke(result);
         } catch (IllegalAccessException e) {
-          throw new AssertionError();
+          throw new AssertionError(e);
         } catch (InvocationTargetException e) {
-          if (e.getCause() instanceof RuntimeException) throw (RuntimeException) e.getCause();
+          if (e.getCause() instanceof RuntimeException) {
+            throw (RuntimeException) e.getCause();
+          }
           throw new RuntimeException(e.getCause());
         }
       }

extras/src/main/java/com/google/gson/typeadapters/UtcDateTypeAdapter.java

@@ -30,7 +30,7 @@
 import java.util.TimeZone;
 
 public final class UtcDateTypeAdapter extends TypeAdapter<Date> {
-  private final TimeZone UTC_TIME_ZONE = TimeZone.getTimeZone("UTC");
+  private static final TimeZone UTC_TIME_ZONE = TimeZone.getTimeZone("UTC");
 
   @Override
   public void write(JsonWriter out, Date date) throws IOException {

extras/src/test/java/com/google/gson/interceptors/InterceptorTest.java

@@ -171,7 +171,9 @@ public void postDeserialize(User user) {
       if (user.name == null || user.password == null) {
         throw new JsonSyntaxException("name and password are required fields.");
       }
-      if (user.email == null) user.email = User.DEFAULT_EMAIL;
+      if (user.email == null) {
+        user.email = User.DEFAULT_EMAIL;
+      }
     }
   }
 
@@ -192,7 +194,9 @@ public void postDeserialize(Address address) {
       if (address.city == null || address.state == null || address.zip == null) {
         throw new JsonSyntaxException("Address city, state and zip are required fields.");
       }
-      if (address.firstLine == null) address.firstLine = Address.DEFAULT_FIRST_LINE;
+      if (address.firstLine == null) {
+        address.firstLine = Address.DEFAULT_FIRST_LINE;
+      }
     }
   }
 }

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

@@ -656,6 +656,16 @@ public <T> TypeAdapter<T> getAdapter(TypeToken<T> type) {
     return candidate;
   }
 
+  /**
+   * Returns the type adapter for {@code type}.
+   *
+   * @throws IllegalArgumentException if this Gson instance cannot serialize and deserialize {@code
+   *     type}.
+   */
+  public <T> TypeAdapter<T> getAdapter(Class<T> type) {
+    return getAdapter(TypeToken.get(type));
+  }
+
   /**
    * This method is used to get an alternate type adapter for the specified type. This is used to
    * access a type adapter that is overridden by a {@link TypeAdapterFactory} that you may have
@@ -748,16 +758,6 @@ public <T> TypeAdapter<T> getDelegateAdapter(TypeAdapterFactory skipPast, TypeTo
     }
   }
 
-  /**
-   * Returns the type adapter for {@code type}.
-   *
-   * @throws IllegalArgumentException if this Gson instance cannot serialize and deserialize {@code
-   *     type}.
-   */
-  public <T> TypeAdapter<T> getAdapter(Class<T> type) {
-    return getAdapter(TypeToken.get(type));
-  }
-
   /**
    * This method serializes the specified object into its equivalent representation as a tree of
    * {@link JsonElement}s. This method should be used when the specified object is not a generic
@@ -983,53 +983,6 @@ public void toJson(JsonElement jsonElement, Appendable writer) throws JsonIOExce
     }
   }
 
-  /**
-   * Returns a new JSON writer configured for the settings on this Gson instance.
-   *
-   * <p>The following settings are considered:
-   *
-   * <ul>
-   *   <li>{@link GsonBuilder#disableHtmlEscaping()}
-   *   <li>{@link GsonBuilder#generateNonExecutableJson()}
-   *   <li>{@link GsonBuilder#serializeNulls()}
-   *   <li>{@link GsonBuilder#setStrictness(Strictness)}. If no {@linkplain
-   *       GsonBuilder#setStrictness(Strictness) explicit strictness has been set} the created
-   *       writer will have a strictness of {@link Strictness#LEGACY_STRICT}. Otherwise, the
-   *       strictness of the {@code Gson} instance will be used for the created writer.
-   *   <li>{@link GsonBuilder#setPrettyPrinting()}
-   *   <li>{@link GsonBuilder#setFormattingStyle(FormattingStyle)}
-   * </ul>
-   */
-  public JsonWriter newJsonWriter(Writer writer) throws IOException {
-    if (generateNonExecutableJson) {
-      writer.write(JSON_NON_EXECUTABLE_PREFIX);
-    }
-    JsonWriter jsonWriter = new JsonWriter(writer);
-    jsonWriter.setFormattingStyle(formattingStyle);
-    jsonWriter.setHtmlSafe(htmlSafe);
-    jsonWriter.setStrictness(strictness == null ? Strictness.LEGACY_STRICT : strictness);
-    jsonWriter.setSerializeNulls(serializeNulls);
-    return jsonWriter;
-  }
-
-  /**
-   * Returns a new JSON reader configured for the settings on this Gson instance.
-   *
-   * <p>The following settings are considered:
-   *
-   * <ul>
-   *   <li>{@link GsonBuilder#setStrictness(Strictness)}. If no {@linkplain
-   *       GsonBuilder#setStrictness(Strictness) explicit strictness has been set} the created
-   *       reader will have a strictness of {@link Strictness#LEGACY_STRICT}. Otherwise, the
-   *       strictness of the {@code Gson} instance will be used for the created reader.
-   * </ul>
-   */
-  public JsonReader newJsonReader(Reader reader) {
-    JsonReader jsonReader = new JsonReader(reader);
-    jsonReader.setStrictness(strictness == null ? Strictness.LEGACY_STRICT : strictness);
-    return jsonReader;
-  }
-
   /**
    * Writes the JSON for {@code jsonElement} to {@code writer}.
    *
@@ -1078,6 +1031,53 @@ public void toJson(JsonElement jsonElement, JsonWriter writer) throws JsonIOExce
     }
   }
 
+  /**
+   * Returns a new JSON writer configured for the settings on this Gson instance.
+   *
+   * <p>The following settings are considered:
+   *
+   * <ul>
+   *   <li>{@link GsonBuilder#disableHtmlEscaping()}
+   *   <li>{@link GsonBuilder#generateNonExecutableJson()}
+   *   <li>{@link GsonBuilder#serializeNulls()}
+   *   <li>{@link GsonBuilder#setStrictness(Strictness)}. If no {@linkplain
+   *       GsonBuilder#setStrictness(Strictness) explicit strictness has been set} the created
+   *       writer will have a strictness of {@link Strictness#LEGACY_STRICT}. Otherwise, the
+   *       strictness of the {@code Gson} instance will be used for the created writer.
+   *   <li>{@link GsonBuilder#setPrettyPrinting()}
+   *   <li>{@link GsonBuilder#setFormattingStyle(FormattingStyle)}
+   * </ul>
+   */
+  public JsonWriter newJsonWriter(Writer writer) throws IOException {
+    if (generateNonExecutableJson) {
+      writer.write(JSON_NON_EXECUTABLE_PREFIX);
+    }
+    JsonWriter jsonWriter = new JsonWriter(writer);
+    jsonWriter.setFormattingStyle(formattingStyle);
+    jsonWriter.setHtmlSafe(htmlSafe);
+    jsonWriter.setStrictness(strictness == null ? Strictness.LEGACY_STRICT : strictness);
+    jsonWriter.setSerializeNulls(serializeNulls);
+    return jsonWriter;
+  }
+
+  /**
+   * Returns a new JSON reader configured for the settings on this Gson instance.
+   *
+   * <p>The following settings are considered:
+   *
+   * <ul>
+   *   <li>{@link GsonBuilder#setStrictness(Strictness)}. If no {@linkplain
+   *       GsonBuilder#setStrictness(Strictness) explicit strictness has been set} the created
+   *       reader will have a strictness of {@link Strictness#LEGACY_STRICT}. Otherwise, the
+   *       strictness of the {@code Gson} instance will be used for the created reader.
+   * </ul>
+   */
+  public JsonReader newJsonReader(Reader reader) {
+    JsonReader jsonReader = new JsonReader(reader);
+    jsonReader.setStrictness(strictness == null ? Strictness.LEGACY_STRICT : strictness);
+    return jsonReader;
+  }
+
   /**
    * This method deserializes the specified JSON into an object of the specified class. It is not
    * suitable to use if the specified class is a generic type since it will not have the generic
@@ -1262,18 +1262,6 @@ public <T> T fromJson(Reader json, TypeToken<T> typeOfT)
     return object;
   }
 
-  private static void assertFullConsumption(Object obj, JsonReader reader) {
-    try {
-      if (obj != null && reader.peek() != JsonToken.END_DOCUMENT) {
-        throw new JsonSyntaxException("JSON document was not fully consumed.");
-      }
-    } catch (MalformedJsonException e) {
-      throw new JsonSyntaxException(e);
-    } catch (IOException e) {
-      throw new JsonIOException(e);
-    }
-  }
-
   // fromJson(JsonReader, Class) is unfortunately missing and cannot be added now without breaking
   // source compatibility in certain cases, see
   // https://github.com/google/gson/pull/1700#discussion_r973764414
@@ -1472,6 +1460,18 @@ public <T> T fromJson(JsonElement json, TypeToken<T> typeOfT) throws JsonSyntaxE
     return fromJson(new JsonTreeReader(json), typeOfT);
   }
 
+  private static void assertFullConsumption(Object obj, JsonReader reader) {
+    try {
+      if (obj != null && reader.peek() != JsonToken.END_DOCUMENT) {
+        throw new JsonSyntaxException("JSON document was not fully consumed.");
+      }
+    } catch (MalformedJsonException e) {
+      throw new JsonSyntaxException(e);
+    } catch (IOException e) {
+      throw new JsonIOException(e);
+    }
+  }
+
   /**
    * Proxy type adapter for cyclic type graphs.
    *

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

@@ -614,14 +614,6 @@ public GsonBuilder setDateFormat(String pattern) {
     return this;
   }
 
-  private static int checkDateFormatStyle(int style) {
-    // Valid DateFormat styles are: 0, 1, 2, 3 (FULL, LONG, MEDIUM, SHORT)
-    if (style < 0 || style > 3) {
-      throw new IllegalArgumentException("Invalid style: " + style);
-    }
-    return style;
-  }
-
   /**
    * Configures Gson to serialize {@code Date} objects according to the date style value provided.
    * You can call this method or {@link #setDateFormat(String)} multiple times, but only the last
@@ -669,6 +661,14 @@ public GsonBuilder setDateFormat(int dateStyle, int timeStyle) {
     return this;
   }
 
+  private static int checkDateFormatStyle(int style) {
+    // Valid DateFormat styles are: 0, 1, 2, 3 (FULL, LONG, MEDIUM, SHORT)
+    if (style < 0 || style > 3) {
+      throw new IllegalArgumentException("Invalid style: " + style);
+    }
+    return style;
+  }
+
   /**
    * Configures Gson for custom serialization or deserialization. This method combines the
    * registration of an {@link TypeAdapter}, {@link InstanceCreator}, {@link JsonSerializer}, and a
@@ -722,7 +722,7 @@ public GsonBuilder registerTypeAdapter(Type type, Object typeAdapter) {
     return this;
   }
 
-  private boolean isTypeObjectOrJsonElement(Type type) {
+  private static boolean isTypeObjectOrJsonElement(Type type) {
     return type instanceof Class
         && (type == Object.class || JsonElement.class.isAssignableFrom((Class<?>) type));
   }
@@ -901,7 +901,7 @@ public Gson create() {
         new ArrayList<>(reflectionFilters));
   }
 
-  private void addTypeAdaptersForDate(
+  private static void addTypeAdaptersForDate(
       String datePattern, int dateStyle, int timeStyle, List<TypeAdapterFactory> factories) {
     TypeAdapterFactory dateAdapterFactory;
     boolean sqlTypesSupported = SqlTypesSupport.SUPPORTS_SQL_TYPES;

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

@@ -38,7 +38,10 @@ public final class JsonPrimitive extends JsonElement {
    *
    * @param bool the value to create the primitive with.
    */
-  @SuppressWarnings("deprecation") // superclass constructor
+  // "deprecation" suppression for superclass constructor
+  // "UnnecessaryBoxedVariable" Error Prone warning is correct since method does not accept
+  // null, but cannot be changed anymore since this is public API
+  @SuppressWarnings({"deprecation", "UnnecessaryBoxedVariable"})
   public JsonPrimitive(Boolean bool) {
     value = Objects.requireNonNull(bool);
   }
@@ -69,7 +72,10 @@ public JsonPrimitive(String string) {
    *
    * @param c the value to create the primitive with.
    */
-  @SuppressWarnings("deprecation") // superclass constructor
+  // "deprecation" suppression for superclass constructor
+  // "UnnecessaryBoxedVariable" Error Prone warning is correct since method does not accept
+  // null, but cannot be changed anymore since this is public API
+  @SuppressWarnings({"deprecation", "UnnecessaryBoxedVariable"})
   public JsonPrimitive(Character c) {
     // convert characters to strings since in JSON, characters are represented as a single
     // character string