Java Swing GUI application is completly blank with no content at all, while buttons are added to the panel

i have built an Swing based GUI, which builds successfully. But after running, it only displays a blank, white frame with no text, button whatsoever on it.

I've already checked that the GUI elements are added to the panel (myPanel.add(bTest, "Card1");). Also the $$$setupUI$$$(); should execute after the constructor.

Code:

package voc;

import javax.swing.*;
import javax.swing.border.TitledBorder;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

public class GUI extends JFrame {
    private JPanel myPanel;
    private JButton bTest;
    private JTextArea tEnterTranslation;

    public GUI() {

        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
        bTest.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                super.mouseClicked(e);
            }
        });
    }

    public static void create() {
        GUI gui = new GUI();
    }


    public static void main(String[] args) {
        create();
    }


    {
// GUI initializer generated by IntelliJ IDEA GUI Designer
// >>> IMPORTANT!! <<<
// DO NOT EDIT OR ADD ANY CODE HERE!
        $$$setupUI$$$();
    }

    /**
     * Method generated by IntelliJ IDEA GUI Designer
     * >>> IMPORTANT!! <<<
     * DO NOT edit this method OR call it in your code!
     *
     * @noinspection ALL
     */
    private void $$$setupUI$$$() {
        myPanel = new JPanel();
        myPanel.setLayout(new CardLayout(0, 0));
        myPanel.setMaximumSize(new Dimension(500, 500));
        myPanel.setMinimumSize(new Dimension(500, 500));
        myPanel.setPreferredSize(new Dimension(500, 500));
        myPanel.setBorder(BorderFactory.createTitledBorder(null, "voc", TitledBorder.DEFAULT_JUSTIFICATION, TitledBorder.DEFAULT_POSITION, new Font(myPanel.getFont().getName(), myPanel.getFont().getStyle(), myPanel.getFont().getSize()), new Color(-4497096)));
        bTest = new JButton();
        bTest.setMinimumSize(new Dimension(10, 20));
        bTest.setText("Button");
        myPanel.add(bTest, "Card1");
        tEnterTranslation = new JTextArea();
        tEnterTranslation.setMinimumSize(new Dimension(20, 15));
        tEnterTranslation.setPreferredSize(new Dimension(20, 15));
        tEnterTranslation.setText("");
        myPanel.add(tEnterTranslation, "Card2");
    }

    /**
     * @noinspection ALL
     */
    public JComponent $$$getRootComponent$$$() {
        return myPanel;
    }
}

You forgot to add the JPanel to your JFrame's contentPane()

public GUI() {
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    this.getContentPane().add(myPanel); <--------------------------------- HERE
    this.setVisible(true);
    bTest.addMouseListener(new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent e) {
            super.mouseClicked(e);
        }
    });
}

Addition

If I were you, I'd also use JFrame#setSize(Dimension) because your JFrame will now appear with the minimum size.