Java Swing UIManager change look and feel

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ItemEvent;
import java.util.Map;
import java.util.TreeMap;
import javax.swing.AbstractButton;
import javax.swing.BorderFactory;
import javax.swing.Box;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JTextField;
import javax.swing.LookAndFeel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UIManager.LookAndFeelInfo;
import javax.swing.border.Border;
import javax.swing.border.EtchedBorder;

public class Main extends JFrame {
  JLabel nameLbl = new JLabel("Name:");
  JTextField nameFld = new JTextField(20);
  JButton saveBtn = new JButton("Save");
  JTextField lafClassNameFld = new JTextField();
  ButtonGroup radioGroup = new ButtonGroup();
  static final Map<String, String> installedLAF = new TreeMap<>();

  static {//w w w. j  ava2s. c o  m
    for (LookAndFeelInfo lafInfo : UIManager.getInstalledLookAndFeels()) {
      installedLAF.put(lafInfo.getName(), lafInfo.getClassName());
    }
  }

  public Main(String title) {
    super(title);
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    Container contentPane = this.getContentPane();

    // Get the current look and feel
    LookAndFeel currentLAF = UIManager.getLookAndFeel();
    String currentLafName = currentLAF.getName();
    String currentLafClassName = currentLAF.getClass().getName();

    lafClassNameFld.setText(currentLafClassName);
    lafClassNameFld.setEditable(false);

    // Build the panels
    JPanel topPanel = buildTopPanel();
    JPanel leftPanel = buildLeftPanel(currentLafName);
    JPanel rightPanel = buildRightPanel();
    contentPane.add(topPanel, BorderLayout.NORTH);
    contentPane.add(leftPanel, BorderLayout.WEST);
    contentPane.add(rightPanel, BorderLayout.CENTER);
  }

  private void setLAF(String lafClassName) {
    try {
      UIManager.setLookAndFeel(lafClassName);
      SwingUtilities.updateComponentTreeUI(this);
      this.pack();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  private JPanel buildTopPanel() {
    JPanel panel = new JPanel();
    panel.add(lafClassNameFld);
    panel.setBorder(getBorder("L&F Class Name"));
    return panel;
  }

  private JPanel buildLeftPanel(String currentLafName) {
    JPanel panel = new JPanel();
    panel.setBorder(getBorder("L&F Name"));
    Box vBox = Box.createVerticalBox();

    // Add a radio button for each installed L&F
    for (String lafName : installedLAF.keySet()) {
      JRadioButton radioBtn = new JRadioButton(lafName);
      if (lafName.equals(currentLafName)) {
        radioBtn.setSelected(true);
      }
      radioBtn.addItemListener(this::changeLAF);
      vBox.add(radioBtn);
      radioGroup.add(radioBtn);
    }

    panel.add(vBox);
    return panel;
  }

  private JPanel buildRightPanel() {
    JPanel panel = new JPanel();
    panel.setBorder(getBorder("Swing Components"));

    Box hBox = Box.createHorizontalBox();
    hBox.add(nameLbl);
    hBox.add(nameFld);
    hBox.add(saveBtn);
    panel.add(hBox);

    return panel;
  }

  private void changeLAF(ItemEvent e) {
    if (e.getSource() instanceof AbstractButton) {
      AbstractButton btn = (AbstractButton) e.getSource();
      String lafName = btn.getText();
      String lafClassName = installedLAF.get(lafName);
      this.lafClassNameFld.setText(lafClassName);
      this.setLAF(lafClassName);
    }
  }

  private Border getBorder(String title) {
    Border etched = BorderFactory.createEtchedBorder(EtchedBorder.LOWERED);
    Border titledBorder = BorderFactory.createTitledBorder(etched, title);
    return titledBorder;
  }

  public static void main(String[] args) {
    SwingUtilities.invokeLater(() -> {
      Main lafApp = new Main("Swing L&F");
      lafApp.pack();
      lafApp.setVisible(true);
    });
  }
}