J2ME and i18n

Resources

• WRITING WORLD-AWARE J2ME APPLICATIONS
• DEALING WITH DATES AND TIMES IN MIDP APPLICATIONS (This is a bit out of date)
• Considerations of globalization solutions in J2ME

Intro

• All computers were once limited resource devices: early PCs had 64k of RAM; Unix was designed as a multi-user system for machines with 64k of RAM; the Apollo space shuttle was controlled by a computer with 32k of RAM
• Current desktop machines are typically 128M RAM with 20G disks or more, and can run heavy languages like Java, C# etc
• Small computers are coming back in many ways: mobile phones, PDAs, sensors, etc
• While some mobile phones are creeping up (64M total memory) this still won't store too much: a Unicode font file can be 16M by itself!

Java VMs

There are several different Java virtual machines now

• The Connected Device Configuration (CDC) is for systems with a reasonable amount of memory: 2M+
• The Connected, Limited Device Configuration (LCDC) is for small devices from 160Kb upwards
• The standard J2SE (Standard Edition) and J2EE (Enterprise Edition) versions remain for large systems such as desktop PCs
• The configurations basically set out the memory constraints of the system
  • CLDC for cellphones, two-way pagers, personal organisers, home appliances, etc
  • CDC for emerging cellphones, point-of-sale terminals, more expensive home appliances, automobile navigation systems, etc

Profiles

• Standard Java J2SDK comes with a set of packages
• Enterprise Java J2EE comes with more
• The smaller Java's have a customisable set of packages called profiles
• The cuurent profiles are listed at J2ME Home

MIDP

• MIDP is the profile targetted for mobile phones Internet Devices
• It assumes CDC plus a mechanism for keyboard input and graphical display
• If you are writing for MIDP and need to show text, German is a good test language since it often produces the longest strings

J2ME i18n support

CLDC support classes

• java.io.DataInputStream
• java.io.DataOutputStream
• java.io.InputStreamReader
• java.io.OutputStreamWriter
• java.io.Reader
• java.io.Writer
• java.util.Calendar
• java.util.Date
• java.util.TimeZone

Reading and writing

• The classes InputStreamReader and OutputStreamReader support at least one encoding, possibly more
• Due to memory constraints they won't support all of the encodings that the J2SE does
• Find the default encoding by

  String encoding = System.getProperty( 
              "microedition.encoding" );
        

Times

• The Calendar, Date and TimeZone classes are subsets of the J2SE classes of the same name. An implementation is only required to support a single time zone, which ideally is the user's local time zone.
• In MIDP, the class DateField can be used for displaying and entering date information

Locale support

• Apart from the classes listed above, the CLDC provides no support for any formatting of strings, numbers, currencies or other locale-specific operations.
• Profiles based on the CLDC are allowed to add more internationalization and localization features
• The Mobile Information Device Profile (MIDP) requires the implementation to define a microedition.locale system property that returns the device's locale in language-country format (as in "en-US" or "fr-FR").
• Also, any HTTP requests that a MIDlet (a Java program that follows the MIDP specifications) makes must set a Content-Encoding header
• There is no input method support
• There is no resource bundle support

JSR 238, Mobile Internationalization API

• This is an optional profile for J2ME devices at http://jcp.org/en/jsr/detail?id=238
• It requires CLDC 1.1 or later
• You can test for the presence of the MI API by getting the system property microedition.global.version. If it is null, the API is not present. It should be "1.0" if it is present
• The API offers no new ideas, it is mainly about optimising the J2SE API
• e.g. there is no Locale class, just strings of the form "LL-CC"
• There is a "reference implementation" from Nokia that only runs with the Nokia J2ME emulator. It will not run with Sun's J2MEWTK (J2ME Wireless Toolkit) due to class loading restrictions

Application resources

• Resources for J2ME programs must be stored in the JAR file for the program
• They cannot be stored in the "file system" since some J2ME devices might not have a file system!
• The format of resources is binary instead of text for space and efficiency
• The binary format is described in JSR-238, and the reference implementation contains a tool to help build them
• Each resource is identified by an integer (a string is used in J2SE), a type (0x01 for string, 0x10 for byte array) e.g.

  0x20 0x01 4F 4B

  is resource number 20 is the string "OK"
• Strings are only in UTF-8

Resource Manager

• The ResourceManager is the way to access application resources
• Relevant methods include

  
        static String[] ResourceManager.getSupportedLocales(String basename);
        static ResourceManager getManager(String baseName, String locale)
        
        byte[] 	getData(int id);
        String 	getString(int id);
        

• You should use sumbolic constants to label the resource ids
• e.g. for application with resources labelled "MyApp"

  
        private static final int OK = 0x20;
        ResourceManager mgr = ResourceManager.getManager("MyApp");
        String okLabel = mgr.getString(OK);
        

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Date and time formatting

• The class Formatter can be used to format dates and strings
• Methods include

  
        Formatter(String locale);
  
        String 	formatCurrency(double number);
        String 	formatDateTime(java.util.Calendar dateTime, int style);
        String 	formatNumber(double number);
        String 	formatPercentage(long value) ;
        

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String Comparison

• There is a class StringComparator
• Comparisons can done by level:
  • LEVEL1: For European languages this level honours differences between alphabetical characters at the language level.
  • LEVEL2: For European languages this level honours differences in normal and accented versions of the same character.
  • LEVEL3: For European languages this level honours differences in character case.
• Methods include

  
        StringComparator();
        StringComparator(String locale);
        StringComparator(String locale, int level);
  
        int 	compare(String s1, String s2);
        boolean 	equals(String s1, String s2) ;
        

• Once you can compare strings, you can sort them by any sorting algorithm and search sorted lists

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Jan Newmarch <jan@newmarch.name>

Last modified: Mon Oct 2 10:13:05 EST 2006
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Copyright © Jan Newmarch, Monash University, 2007
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