Java Cookbook

Storing Strings in Properties and Preferences

Problem

You need to store keys and values that are both strings, possibly with persistence across runs of a program. For example: program customization.

Solution

Use a java.util.Properties object (or a java.util.Prefs.Preferences object in JDK 1.4).

Discussion

The Properties class is similar to a HashMap or Hashtable (it extends the latter), but with methods defined specifically for string storage and retrieval and for loading/saving. Properties objects are used throughout Java, for everything from setting the platform font names to customizing user applications into different Locale settings as part of internationalization and localization. When stored on disk, a Properties object looks just like a series of name=value assignments, with optional comments. Comments are added when you hand-edit a Properties file, ignored when the Properties object reads itself, and lost when you ask the Properties object to save itself to disk. Here is an example of a Properties file that could be used to internationalize the menus in a GUI-based program:

# Default properties for MenuIntl
program.title=Demonstrate I18N (MenuIntl)
program.message=Welcome to an English-localized Java Program
#
# The File Menu
#
file.label=File Menu
file.new.label=New File
file.new.key=N
file.open.label=Open...
file.open.key=O
file.save.label=Save
file.save.key=S
file.exit.label=Exit
file.exit.key=Q

Here is another example, showing some personalization properties:

name=Ian ...