Using the preference API in Java. This tutorial gives a introduction into the Java Preference API to save key/value pairs for a Java application.
1. Java Preferences API
The Java Preferences API provides a systematic way to handle program preference configurations, e.g. to save user settings, remember the last value of a field etc.
Preferences are key / values pairs where the key is an arbitrary name for the preference. The value can be a boolean, string, int of another primitive type. Preferences are received and saved by get and put methods while the get methods also supply a default value in case the preferences is not yet set.
| This Java Preferences API is not indented to save application data, i.e. larger structured data. |
The Java Preference API removes the burden from the individual programmer to write code to save configuration values on the different platforms his program may be running.
The actual storage of the data is dependent on the platform.
2. Exercise: Using the API
2.1. Create program
java.util.prefs.Preferences can be easily used.
You have to define a node in which the data is stored.
Then you can call the getter and setter methods.
The second value is the default value, e.g. if the preference value is not set yet, then this value will be used.
Create the following program.
import java.util.prefs.Preferences;
public class PreferenceTest {
private Preferences prefs;
public void setPreference() {
// This will define a node in which the preferences can be stored
prefs = Preferences.userRoot().node(this.getClass().getName());
String ID1 = "Test1";
String ID2 = "Test2";
String ID3 = "Test3";
// First we will get the values
// Define a boolean value
System.out.println(prefs.getBoolean(ID1, true));
// Define a string with default "Hello World
System.out.println(prefs.get(ID2, "Hello World"));
// Define a integer with default 50
System.out.println(prefs.getInt(ID3, 50));
// now set the values
prefs.putBoolean(ID1, false);
prefs.put(ID2, "Hello Europa");
prefs.putInt(ID3, 45);
// Delete the preference settings for the first value
prefs.remove(ID1);
}
public static void main(String[] args) {
PreferenceTest test = new PreferenceTest();
test.setPreference();
}
}2.2. Validate
Run the program twice. The value of "ID1" should be written with its default value (true) to the command line, as the preference value was deleted at the end of the method. The value of "ID2" and "ID3" should have changed after the first call.
3. Links and Literature
Nothing listed.
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