The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
A compound message may contain several kinds of variables: dates, times, strings, numbers, currencies, and percentages. To format a compound message in a locale-independent manner, you construct a pattern that you apply to a MessageFormat
object, and store this pattern in a ResourceBundle
.
By stepping through a sample program, this section demonstrates how to internationalize a compound message. The sample program makes use of the
MessageFormat
class. The full source code for this program is in the file called
MessageFormatDemo.java
. The German locale properties are in the file called
MessageBundle_de_DE.properties
.
Suppose that you want to internationalize the following message:
Notice that we've underlined the variable data and have identified what kind of objects will represent this data.
Store the message in a ResourceBundle
named MessageBundle
, as follows:
ResourceBundle messages = ResourceBundle.getBundle("MessageBundle", currentLocale);
This ResourceBundle
is backed by a properties file for each Locale
. Since the ResourceBundle
is called MessageBundle
, the properties file for U.S. English is named MessageBundle_en_US.properties
. The contents of this file is as follows:
template = At {2,time,short} on {2,date,long}, \ we detected {1,number,integer} spaceships on \ the planet {0}. planet = Mars
The first line of the properties file contains the message pattern. If you compare this pattern with the message text shown in step 1, you'll see that an argument enclosed in braces replaces each variable in the message text. Each argument starts with a digit called the argument number, which matches the index of an element in an Object
array that holds the argument values. Note that in the pattern the argument numbers are not in any particular order. You can place the arguments anywhere in the pattern. The only requirement is that the argument number have a matching element in the array of argument values.
The next step discusses the argument value array, but first let's look at each of the arguments in the pattern. The following table provides some details about the arguments:
Argument | Description |
---|---|
{2,time,short} |
The time portion of a Date object. The short style specifies the DateFormat.SHORT formatting style. |
{2,date,long} |
The date portion of a Date object. The same Date object is used for both the date and time variables. In the Object array of arguments the index of the element holding the Date object is 2. (This is described in the next step.) |
{1,number,integer} |
A Number object, further qualified with the integer number style. |
{0} |
The String in the ResourceBundle that corresponds to the planet key. |
For a full description of the argument syntax, see the API documentation for the
MessageFormat
class.
The following lines of code assign values to each argument in the pattern. The indexes of the elements in the messageArguments
array match the argument numbers in the pattern. For example, the Integer
element at index 1 corresponds to the {1,number,integer}
argument in the pattern. Because it must be translated, the String
object at element 0 will be fetched from the ResourceBundle
with the getString
method. Here is the code that defines the array of message arguments:
Object[] messageArguments = { messages.getString("planet"), new Integer(7), new Date() };
Next, create a MessageFormat
object. You set the Locale
because the message contains Date
and Number
objects, which should be formatted in a locale-sensitive manner.
MessageFormat formatter = new MessageFormat(""); formatter.setLocale(currentLocale);
This step shows how the pattern, message arguments, and formatter all work together. First, fetch the pattern String
from the ResourceBundle
with the getString
method. The key to the pattern is template
. Pass the pattern String
to the formatter with the applyPattern
method. Then format the message using the array of message arguments, by invoking the format
method. The String
returned by the format
method is ready to be displayed. All of this is accomplished with just two lines of code:
formatter.applyPattern(messages.getString("template")); String output = formatter.format(messageArguments);
The demo program prints the translated messages for the English and German locales and properly formats the date and time variables. Note that the English and German verbs ("detected" and "entdeckt") are in different locations relative to the variables:
currentLocale = en_US At 10:16 AM on July 31, 2009, we detected 7 spaceships on the planet Mars. currentLocale = de_DE Um 10:16 am 31. Juli 2009 haben wir 7 Raumschiffe auf dem Planeten Mars entdeckt.