Java Glossary : preferences

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preferences

java.util.prefs.Preferences appeared in Java 1.4.1 as way to store configuration data for applications and individual users. Unfortunately, in windows this information is stored in the fragile, hard-to-back-up registry in HKEY_LOCAL_MACHINE\JavaSoft\Prefs for system preferences and HKEY_CURRENT_USER\JavaSoft\Prefs for user preferences.

On Linux, they are stored in the file system in the /etc/.java directory for system preferences and the ~/.java directory for user preferences.

In theory, a JVM could hide them in an SQL database or any other scheme it concocted.

Here is how you use them:

import java.util.prefs. Preferences;
...
// get object for storing preferences for MyClass
private Preferences userPrefs =
Preferences.userNodeForPackage ( MyClass.class );
...
// store preferences, key=value
userPrefs.putInt( "width" , width );
userPrefs.putInt( "height", height );
...
// fetch preferences, key,default
int width = userPrefs.getInt( "width", 100 );
int height = userPrefs.getInt( "height", 200 );

systemNodeForPackage lets you specify preferences for the whole machine for each package. userNodeForPackage lets you specify preferences for a particular user for that package. If the package is used in more than one context, e.g. the same class used in two different programs or the same class is used to manage two separate sets of files, it is up to you to create another level of name to keep track of the context. Note though you specify a class name, the preferences are on a per package, not a per class basis.

User preferences show up at My_Computer\HKEY_CURRENT_USER\Software\JavaSoft\Prefs\com\mindprod\replicator and My_Computer\HKEY_USERS\usernamexxx\Software\JavaSoft\Prefs\com\mindprod\replicator where the package name is com.mindprod.replicator.

System preferences show up at My_Computer\HKEY_LOCAL_MACHINE\Software\JavaSoft\Prefs\com\mindprod\replicator.

The registry will be more legible with regedit if you stick to lower case keys and values.

Using Preferences : available:

on the web at java.Sun.com
on J: in the JDK 1.4.2_04: J:\j2sdk1.4.2_04\docs\api\java\util\prefs\Preferences.html
on J: in the JDK 1.5 beta: J:\Program Files\Java\j2sdk1.5.0\docs\api\java\util\prefs\Preferences.html

properties ¤ registry

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