JButton won't show text

Question

This class represents the button panel of a UI I have created, the second JButton named 'btnNext' doesn't display text however the first JButton does, why is this?

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;

public class ButtonPanel extends JPanel {
    private MainPanel mainPanel;

    // Buttons
    private JButton btnRunTheAlgorithm = new JButton("Run the Algorithm");
    public static JButton btnNext = new JButton("Next Step");

    public ButtonPanel(MainPanel mainPanel) {
        this.mainPanel = mainPanel;
        this.setLayout(new FlowLayout());
        this.add(btnRunTheAlgorithm);
        this.add(btnNext);


        this.btnRunTheAlgorithm.addActionListener(e -> {
            Algorithm main = new Algorithm(mainPanel);
            main.Run();
        });

        this.btnNext.setAction(new AbstractAction() {
            public void actionPerformed(ActionEvent ae) {
                synchronized (btnNext) {
                    btnNext.notify();
                }
             }
         });
     }
 }

The buttons displays to the panel as on the image below:

Buttons:

I'm also not sure the AbstractAction works, so I suppose that could be the cause of the text not displaying but I have no idea why if that is the case.