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DEALING WITH DATES AND TIMES IN MIDP APPLICATIONS (This is a bit out of date)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);






 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) ;
      
  





 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
  








Jan Newmarch <jan@newmarch.name>

Last modified: Mon Oct  2 10:13:05 EST 2006


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