What is the component of pluggable look and feel in java?

Answer 1

"Pluggable look and feel" refers to the ability to change the look and feel (LnF) of a Java program on the fly. The term is actually quite descriptive. If you change the LnF of your program, all GUI elements will have a distinctly different look to them. Windows will be drawn differently, buttons and scroll bars will look (and may respond) differently, etc.

You can change the current LnF by invoking:

UIManager.setLookAndFeel(lookAndFeel);

Probably the most useful invocation of this method uses the UIManager class to figure out what the underlying operating system is, and to use the default LnF for your program:

UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

This will make programs run on a Windows machine look like a Windows application, programs run on a Mac look like a Mac application, etc.

Another useful function is the UIManager.getInstalledLookAndFeels(), which will return an array of all available LnFs.

Below is a simple sample program which will demonstrate these methods.

Two things to take note of:

# Once you change the look and feel, you need to call the updateUI method on all JComponents. The good people at Sun recommend calling SwingUtilities.updateComponentTreeUI(Component). If you call this on your top level components (main frame/window), it should update all components contained within it. # UIManager.setLookAndFeel can throw a lot of exceptions. Be prepared to have a large try-catch block (or a throws clause) everywhere you set the LnF.

try {

// Start off with the system default LnF

UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

// Ugly, ugly try-catch block if you catch each type individually.

} catch (final ClassNotFoundException ex) {

} catch (final InstantiationException ex) {

} catch (final IllegalAccessException ex) {

} catch (final UnsupportedLookAndFeelException ex) {

} catch (final ClassCastException ex) {

}

// Create our frame

final JFrame frame = new JFrame("LnF Test Frame");

// Set up our simple panel

final JPanel panel = new JPanel();

panel.setLayout(new GridLayout(4, 4));

// Set up a button for each installed LookAndFeel.

// When a button is pressed, the LnF will change.

for (final LookAndFeelInfo lnfInfo : UIManager.getInstalledLookAndFeels()) {

final String lnfName = lnfInfo.getName();

final String lnfClassName = lnfInfo.getClassName();

final JButton button = new JButton(lnfName);

button.addActionListener(new ActionListener() {

// Here's where we change and update the LnF

public final void actionPerformed(final ActionEvent ev) {

try {

UIManager.setLookAndFeel(lnfClassName);

SwingUtilities.updateComponentTreeUI(frame);

} catch (final Exception ex) {

}

}

});

panel.add(button);

}

// Set up and display our frame

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

// (adding a scroll panel just to see some more components)

frame.setContentPane(new JScrollPane(panel, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS));

frame.setSize(300, 300);

frame.setVisible(true);