What is the name of the design pattern used in AWT/Swing that handles events?

Question

I have heard that there are 2 ways that we can set the PLAF in Swing. What is the real meaning of PLAF, and what are those 2 ways?

Answer 1

Observer Pattern.

Some of the most notable implementations of this pattern:

• The Java Swing library makes extensive use of the observer pattern for event management.

Answer 2

To answer the question in your title: Observer is the design pattern that Swing employs.

PLAF is a 'Pluggable Look And Feel'. Here is a reference for PLAF in Java.

The title, regarding the Event Listeners, and the PLAF are not related. The former has to do with the processing of events - more closely associated with the C in MVC, while the latter is generally associated with the View aspect of MVC.

Answer 3

PLAF = Pluggable Look and Feel. Basically, the same UI can have different skins with very little work.

Check out this site for a detailed description of L&F. In short, there are actually 3 ways to set up your PLAF.

1) Via command line: java -Dswing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel MyApp or java -Dswing.defaultlaf=com.sun.java.swing.plaf.windows.WindowsLookAndFeel MyApp

2) Via swing.properties file in your java lib. swing.defaultlaf=com.sun.java.swing.plaf.windows.WindowsLookAndFeel

3) Programatically with either:

//At the beginning of your program
UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName());
//Another option
UIManager.setLookAndFeel("com.sun.java.swing.plaf.motif.MotifLookAndFeel");
//And another
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

//Or during your program - 
UIManager.setLookAndFeel(lnfName);
SwingUtilities.updateComponentTreeUI(frame);
frame.pack();

The above link also has code examples to demonstrate how to change your look and feel.

Hope that helps!