com.google.gwt.i18n.client
Interface Messages

All Superinterfaces:

Localizable, LocalizableResource

All Known Subinterfaces:

CellTree.CellTreeMessages

public interface Messages
extends LocalizableResource

A tag interface that facilitates locale-sensitive, compile-time binding of messages supplied from various sources.Using GWT.create(class) to "instantiate" an interface that extends Messages returns an instance of an automatically generated subclass that is implemented using message templates selected based on locale. Message templates are based on a subset of the format used by MessageFormat. Note in particular that single quotes are used to quote other characters, and should be doubled for a literal single quote.

Locale is specified at run time using a meta tag or query string as described for Localizable.

Extending Messages

public interface GameStatusMessages extends Messages {
  /**
   * @param username the name of a player
   * @param numTurns the number of turns remaining
   * @return a message specifying the remaining turns for a player
   */
  String turnsLeft(String username, int numTurns);

  /**
   * @param numPoints the number of points
   * @return a message describing the current score for the current player
   */
  String currentScore(int numPoints);
}

turnsLeft = Turns left for player ''{0}'': {1}
currentScore = Current score: {0}

The following example demonstrates how to use constant accessors defined in the interface above:

public void beginNewGameRound(String username) {
  GameStatusMessages messages = (GameStatusMessages) GWT.create(GameStatusMessages.class);

  // Tell the new player how many turns he or she has left.
  int turnsLeft = computeTurnsLeftForPlayer(username);
  showMessage(messages.turnsLeft(username, turnsLeft));

  // Tell the current player his or her score.
  int currentScore = computeScore(username);
  setCurrentPlayer(username);
  showMessage(messages.currentScore(currentScore));
}

The following example shows how to use annotations to store the default strings in the source file itself, rather than needing a properties file (you still need properties files for the translated strings):

public interface GameStatusMessagesAnnot extends Messages {
  /**
   * @param username the name of a player
   * @param numTurns the number of turns remaining
   * @return a message specifying the remaining turns for a player
   */
  @DefaultMessage("Turns left for player ''{0}'': {1}")
  String turnsLeft(String username, int numTurns);

  /**
   * @param numPoints the number of points
   * @return a message describing the current score for the current player
   */
  @DefaultMessage("Current score: {0}")
  String currentScore(int numPoints);
}

In this example, calling msg.turnsLeft("John", 13) would return the string "Turns left for player 'John': 13".

Defining Message Accessors

String methodName(optional-params)

Compile-time checks are performed to ensure that the number of placeholders in a message template (e.g. {0}) matches the number of parameters supplied.

Integral arguments may be used to select the proper plural form to use for different locales. To do this, mark the particular argument with @PluralCount (a plural rule may be specified with @PluralCount if necessary, but you will almost never need to do this). The actual plural forms for the default locale can be supplied in a @PluralText annotation on the method, such as @PluralText({"one", "You have one widget"}), or they can be supplied in the properties file as methodkey[one]=You have one widget. Note that non-default plural forms are not inherited between locales, because the different locales may have different plural rules (especially default and anything else and those which use different scripts such as sr_Cyrl and sr_Latn [one of which would likely be the default], but also subtle cases like pt and pt_BR).

Additionally, individual arguments can be marked as optional (ie, GWT will not give an error if a particular translation does not reference the argument) with the @Optional annotation, and an example may be supplied to the translator with the @Example(String) annotation.

Complete Annotations Example

 @Generate(format = "com.google.gwt.i18n.rebind.format.PropertiesFormat")
 @DefaultLocale("en_US")
 public interface MyMessages extends Messages {
   @Key("1234")
   @DefaultMessage("This is a plain string.")
   String oneTwoThreeFour();
   
   @DefaultMessage("You have {0} widgets")
   @PluralText({"one", "You have one widget")
   String widgetCount(@PluralCount int count);
   
   @DefaultMessage("No reference to the argument")
   String optionalArg(@Optional String ignored);
   
   @DefaultMessage("Your cart total is {0,number,currency}")
   @Description("The total value of the items in the shopping cart in local currency")
   String totalAmount(@Example("$5.00") double amount);
   
   @Meaning("the color")
   @DefaultMessage("orange")
   String orangeColor();
   
   @Meaning("the fruit")
   @DefaultMessage("orange")
   String orangeFruit();
 }
 

Binding to Properties Files

Required Module

<module>
  <!-- other inherited modules, such as com.google.gwt.user.User -->
  <inherits name="com.google.gwt.i18n.I18N"/>
  <!-- additional module settings -->
</module>

Note