Пожалуйста, есть другой способ, как изменить шрифт во время выполнения, используя FontUIResource, для всего графического интерфейса AWT / Swing, без каких-либо знаний / интереса о наличии локальных переменных и типа JComponents

import java.awt.*;
import java.awt.event.*;
import java.util.Locale;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.*;
import javax.swing.plaf.FontUIResource;
import javax.swing.plaf.basic.BasicComboBoxRenderer;

public class SystemFontDisplayer extends JFrame {

    private static final long serialVersionUID = 1L;
    private JFrame frame = new JFrame("Nimbus UIDeafaults and Font");
    private JComboBox fontsBox;
    private javax.swing.Timer timer = null;
    private JButton testButton = new JButton("testButton");
    private JTextField testTextField = new JTextField("testTextField");
    private JLabel testLabel = new JLabel("testLabel");

    public SystemFontDisplayer() {
        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        String[] fontFamilyNames = ge.getAvailableFontFamilyNames(Locale.getDefault());
        fontsBox = new JComboBox(fontFamilyNames);
        fontsBox.setSelectedItem(0);
        fontsBox.setRenderer(new ComboRenderer());
        fontsBox.addItemListener(new ItemListener() {

            @Override
            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == ItemEvent.SELECTED) {
                    final String fontName = fontsBox.getSelectedItem().toString();
                    fontsBox.setFont(new Font(fontName, Font.PLAIN, 16));
                    start();
                }
            }
        });
        fontsBox.setSelectedItem(0);
        fontsBox.getEditor().selectAll();
        frame.setLayout(new GridLayout(4, 0, 20, 20));
        frame.add(fontsBox);
        frame.add(testButton);
        frame.add(testTextField);
        frame.add(testLabel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocation(200, 105);
        frame.pack();
        java.awt.EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                fontsBox.setPopupVisible(true);
                fontsBox.setPopupVisible(false);
            }
        });
        frame.setVisible(true);
    }

    private void start() {
        timer = new javax.swing.Timer(750, updateCol());
        timer.setRepeats(false);
        timer.start();
    }

    public Action updateCol() {
        return new AbstractAction("text load action") {

            private static final long serialVersionUID = 1L;

            @Override
            public void actionPerformed(ActionEvent e) {
                final Font fnt = new Font(fontsBox.getSelectedItem().toString(), Font.PLAIN, 12);
                /*try {
                    LookAndFeel lnf = UIManager.getLookAndFeel().getClass().newInstance();
                    final FontUIResource res = new FontUIResource(fnt);
                    UIDefaults uiDefaults = lnf.getDefaults();
                    uiDefaults.put("Button.font", res);
                    uiDefaults.put("TextField.font", res);
                    uiDefaults.put("Label.font", res);
                    UIManager.getLookAndFeel().uninitialize();
                    UIManager.setLookAndFeel(lnf);
                } catch (InstantiationException ex) {
                    Logger.getLogger(SystemFontDisplayer.class.getName()).log(Level.SEVERE, null, ex);
                } catch (IllegalAccessException ex) {
                    Logger.getLogger(SystemFontDisplayer.class.getName()).log(Level.SEVERE, null, ex);
                } catch (UnsupportedLookAndFeelException ex) {
                    Logger.getLogger(SystemFontDisplayer.class.getName()).log(Level.SEVERE, null, ex);
                }
                UIDefaults defaults = UIManager.getDefaults();
                final FontUIResource res = new FontUIResource(fnt);
                defaults.put("Button.font", res);
                defaults.put("TextField.font", res);
                defaults.put("Label.font", res);
                SwingUtilities.updateComponentTreeUI(frame);*/
                final FontUIResource res = new FontUIResource(fnt);
                UIManager.getLookAndFeelDefaults().put("Button.font", res);
                UIManager.getLookAndFeelDefaults().put("TextField.font", res);
                UIManager.getLookAndFeelDefaults().put("Label.font", res);
                SwingUtilities.updateComponentTreeUI(frame);
            }
        };
    }

    public static void main(String arg[]) {
        /*try {
            for (UIManager.LookAndFeelInfo laf : UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(laf.getName())) {
                    UIManager.setLookAndFeel(laf.getClassName());
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }*/
        java.awt.EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                SystemFontDisplayer systemFontDisplayer = new SystemFontDisplayer();
            }
        });
    }

    private class ComboRenderer extends BasicComboBoxRenderer {

        private static final long serialVersionUID = 1L;

        @Override
        public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
            super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
            final Object fntObj = value;
            final String fontFamilyName = (String) fntObj;
            setFont(new Font(fontFamilyName, Font.PLAIN, 16));
            return this;
        }
    }
}

.

РЕДАКТИРОВАТЬ: я опубликовал рассказ с Nimbus, а затем код для Nimbus

import java.awt.*;
import java.awt.event.*;
import java.util.Locale;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.*;
import javax.swing.plaf.FontUIResource;
import javax.swing.plaf.basic.BasicComboBoxRenderer;

public class SystemFontDisplayer extends JFrame {

    private static final long serialVersionUID = 1L;
    private JFrame frame = new JFrame("Nimbus UIDeafaults and Font");
    private JComboBox fontsBox;
    private javax.swing.Timer timer = null;
    private JButton testButton = new JButton("testButton");
    private JTextField testTextField = new JTextField("testTextField");
    private JLabel testLabel = new JLabel("testLabel");

    public SystemFontDisplayer() {
        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        String[] fontFamilyNames = ge.getAvailableFontFamilyNames(Locale.getDefault());
        fontsBox = new JComboBox(fontFamilyNames);
        fontsBox.setSelectedItem(0);
        fontsBox.setRenderer(new ComboRenderer());
        fontsBox.addItemListener(new ItemListener() {

            @Override
            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == ItemEvent.SELECTED) {
                    final String fontName = fontsBox.getSelectedItem().toString();
                    fontsBox.setFont(new Font(fontName, Font.PLAIN, 16));
                    start();
                }
            }
        });
        fontsBox.setSelectedItem(0);
        fontsBox.getEditor().selectAll();
        frame.setLayout(new GridLayout(4, 0, 20, 20));
        frame.add(fontsBox);
        frame.add(testButton);
        frame.add(testTextField);
        frame.add(testLabel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocation(200, 105);
        frame.pack();
        java.awt.EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                fontsBox.setPopupVisible(true);
                fontsBox.setPopupVisible(false);
            }
        });
        frame.setVisible(true);
    }

    private void start() {
        timer = new javax.swing.Timer(750, updateCol());
        timer.setRepeats(false);
        timer.start();
    }

    public Action updateCol() {
        return new AbstractAction("text load action") {

            private static final long serialVersionUID = 1L;

            @Override
            public void actionPerformed(ActionEvent e) {
                final Font fnt = new Font(fontsBox.getSelectedItem().toString(), Font.PLAIN, 12);
                try {
                    LookAndFeel lnf = UIManager.getLookAndFeel().getClass().newInstance();
                    final FontUIResource res = new FontUIResource(fnt);
                    UIDefaults uiDefaults = lnf.getDefaults();
                    uiDefaults.put("Button.font", res);
                    uiDefaults.put("TextField.font", res);
                    uiDefaults.put("Label.font", res);
                    UIManager.getLookAndFeel().uninitialize();
                    UIManager.setLookAndFeel(lnf);
                } catch (InstantiationException ex) {
                    Logger.getLogger(SystemFontDisplayer.class.getName()).log(Level.SEVERE, null, ex);
                } catch (IllegalAccessException ex) {
                    Logger.getLogger(SystemFontDisplayer.class.getName()).log(Level.SEVERE, null, ex);
                } catch (UnsupportedLookAndFeelException ex) {
                    Logger.getLogger(SystemFontDisplayer.class.getName()).log(Level.SEVERE, null, ex);
                }
                UIDefaults defaults = UIManager.getDefaults();
                final FontUIResource res = new FontUIResource(fnt);
                defaults.put("Button.font", res);
                defaults.put("TextField.font", res);
                defaults.put("Label.font", res);
                SwingUtilities.updateComponentTreeUI(frame);
                /*final FontUIResource res = new FontUIResource(fnt);
                UIManager.getLookAndFeelDefaults().put("Button.font", res);
                UIManager.getLookAndFeelDefaults().put("TextField.font", res);
                UIManager.getLookAndFeelDefaults().put("Label.font", res);
                SwingUtilities.updateComponentTreeUI(frame);*/
            }
        };
    }

    public static void main(String arg[]) {
        try {
            for (UIManager.LookAndFeelInfo laf : UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(laf.getName())) {
                    UIManager.setLookAndFeel(laf.getClassName());
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        java.awt.EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                SystemFontDisplayer systemFontDisplayer = new SystemFontDisplayer();
            }
        });
    }

    private class ComboRenderer extends BasicComboBoxRenderer {

        private static final long serialVersionUID = 1L;

        @Override
        public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
            super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
            final Object fntObj = value;
            final String fontFamilyName = (String) fntObj;
            setFont(new Font(fontFamilyName, Font.PLAIN, 16));
            return this;
        }
    }
}