A Java Preferences API example/tutorial

Using the Java Preferences API couldn’t be much easier. In a Swing application I was just working on I wanted to remember the last output directory a user accessed, and the following steps show all that I had to do:

Step 1: Import the Java Preferences package:

import java.util.prefs.*;

Step 2:  Create a Java Preferences reference

Next, just create a Preferences object instance. I usually do this in a main class, main controller, or a “preferences controller,” depending on the size of the application:

// declare my variable at the top of my Java class
private Preferences prefs;

// create a Preferences instance (somewhere later in the code)
prefs = Preferences.userNodeForPackage(this.getClass());

Step 3: Set the preference when a desired action occurs

In the next section of code I’m going to “remember” the last directory a user selected when the user presses a button. I don’t have a screen shot here, but the UI looks like a typical file/directory selection widget, with a textfield and a lookup button next to each other.

void outputDirectoryButton_actionPerformed(ActionEvent e)
  int status = getDirectoryFromUser(jFileChooser,mostRecentOutputDirectory);
  if ( status == JFileChooser.APPROVE_OPTION )
    mostRecentOutputDirectory = jFileChooser.getSelectedFile();
    prefs.put("LAST_OUTPUT_DIR", mostRecentOutputDirectory.getAbsolutePath());

Step 4: Get the reference to pre-populate a textfield the next time the user comes to the desired data entry screen

Now, whenever the user comes back to the UI again, I can pre-populate the textfield with the last directory they chose, using the code below:

String lastOutputDir = prefs.get("LAST_OUTPUT_DIR", "");

Java Preferences - verification

To see what the Preferences API is doing for me, I looked at my Windows registry with regedit. The key name that was created for me is:


When I poke through the registry and get to this node, I find my “LAST_OUTPUT_DIR” key.

Again, this is pretty simple and straightforward, and I encourage you to use the Preferences API to do things like this that make your application more user-friendly.

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