google/gson · error · IllegalArgumentException

Invalid style

Error message

Invalid style: ${style}

What it means

Thrown by GsonBuilder.checkDateFormatStyle(int) when a date/time style passed to setDateFormat(int) or setDateFormat(int,int) is outside 0..3. Only FULL(0), LONG(1), MEDIUM(2), SHORT(3) are valid DateFormat style constants; anything else is rejected with an IllegalArgumentException at configuration time.

Solutions

1. Use one of DateFormat.FULL, DateFormat.LONG, DateFormat.MEDIUM, DateFormat.SHORT.
2. If you need a custom format, use setDateFormat(String pattern) instead of the int style overload.
3. Validate the constant before calling: ensure it is within 0..3 inclusive.

Example fix

// before
builder.setDateFormat(DateFormat.DEFAULT); // -1 -> throws

// after
builder.setDateFormat(DateFormat.MEDIUM, DateFormat.SHORT);

// Validate style constant before calling
static boolean validStyle(int s) { return s >= 0 && s <= 3; }
if (!validStyle(dateStyle) || !validStyle(timeStyle)) {
  throw new IllegalArgumentException("style must be one of FULL(0),LONG(1),MEDIUM(2),SHORT(3)");
}
builder.setDateFormat(dateStyle, timeStyle);

try { builder.setDateFormat(dateStyle, timeStyle); }
catch (IllegalArgumentException e) {
  if (e.getMessage().startsWith("Invalid style")) { /* use a valid constant or pattern */ }
  else throw e;
}

When it happens

Trigger: Passing a style value of 4 or higher; passing a negative value; passing an unrelated constant (e.g. a Locale or Calendar constant) by mistake; passing DEFAULT (which is -1 in DateFormat and invalid here).

Common situations: Using DateFormat.DEFAULT (= -1) thinking it is valid; arithmetic on style values that goes out of range; copying a constant from a different enum.

Related errors

• Invalid version
• The date pattern ' ' is not valid
• Class does not implement any supported type adapter class…
• Only combinations of \n and \r are allowed in newline.
• Only combinations of spaces and tabs are allowed in indent.

AI-assisted analysis of google/gson@310ac341f2 (2026-08-10). Data as JSON: /api/errors/13c6e4d53d6bd978. Report an issue: GitHub.

Appendix: source

Thrown at gson/src/main/java/com/google/gson/GsonBuilder.java:707

   * @param dateStyle the predefined date style that date objects will be serialized/deserialized
   *     to/from
   * @param timeStyle the predefined style for the time portion of the date objects
   * @return a reference to this {@code GsonBuilder} object to fulfill the "Builder" pattern
   * @throws IllegalArgumentException if the style values are invalid
   * @since 1.2
   */
  @CanIgnoreReturnValue
  public GsonBuilder setDateFormat(int dateStyle, int timeStyle) {
    this.dateStyle = checkDateFormatStyle(dateStyle);
    this.timeStyle = checkDateFormatStyle(timeStyle);
    this.datePattern = null;
    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
   * {@link JsonDeserializer}. It is best used when a single object {@code typeAdapter} implements
   * all the required interfaces for custom serialization with Gson. If a type adapter was
   * previously registered for the specified {@code type}, it is overwritten.
   *
   * <p>This registers the type specified and no other types: you must manually register related
   * types! For example, applications registering {@code boolean.class} should also register {@code
   * Boolean.class}. And when registering an adapter for a class which has subclasses, you might
   * also want to register the adapter for subclasses, or use {@link
   * #registerTypeHierarchyAdapter(Class, Object)} instead.
   *
   * <p>{@link JsonSerializer} and {@link JsonDeserializer} are made "{@code null}-safe". This means

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