Learning Java, 4th Edition

The Preferences API

The Java Preferences API accommodates the need to store both system and per-user configuration data persistently across executions of the Java VM. The Preferences API is like a portable version of the Windows registry, a mini-database in which you can keep small amounts of information, accessible to all applications. Entries are stored as name/value pairs, where the values may be of several standard types including strings, numbers, Booleans, and even short byte arrays. We should stress that the Preferences API is not intended to be used as a true database and you can’t store large amounts of data in it.

Preferences are stored logically in a tree. A preferences object is a node in the tree located by a unique path. You can think of preferences as files in a directory structure; within the file are stored one or more name/value pairs. To store or retrieve items, you ask for a preferences object for the correct path. Here is an example; we’ll explain the node lookup shortly:

    Preferences prefs = Preferences.userRoot().node("oreilly/learningjava");

    prefs.put("author", "Niemeyer");
    prefs.putInt("edition", 4);

    String author = prefs.get("author", "unknown");
    int edition = prefs.getInt("edition", -1);

In addition to the String and int type accessors, there are the following get methods for other types: getLong(), getFloat(), getDouble(), getByteArray(), and getBoolean(). Each of these get methods takes a key name and default value to be used if no value is defined. And, ...