除非鼠标悬停，否则JButton不会出现

Question

我制作了一个数独游戏程序，但我有一个问题我无法解决。我总共有4个按钮但只有一个按钮出现，除非我将鼠标悬停在其他按钮上。我知道这与setLayout选项有关，但我不知道如何修复它而不会弄乱我的显示。我通常不会要求一个完整的解决方案，但如果有人能给我一个大手，那么我将非常感谢它。对不起，代码很大......我在这个项目的最后，我真的迷失了这个最后的问题。这是按钮发生的主要部分：

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.border.Border;

public class Test extends JFrame implements ActionListener{

public static JPanel Container1;
public static JPanel Container2;
public static JPanel containermain;
public static JLabel FOND_ECRAN;
public static JButton verify = new JButton("Verify");
public static JButton solve = new JButton("Solve");
public static JButton reset = new JButton("Reset");
public static JButton submit = new JButton("Submit");
public static JTextField [][] cases= new  JTextField [9][9];
public static int [][] NOMBRES_DEBUT;

public static void main(String[] args) {
    Test t = new Test();
}

public Test(){
    NOMBRES_DEBUT = new int[9][9];
    //Permet d'avoir une fenêtre en plein-écran
    //this.setUndecorated(true); 
    this.setAlwaysOnTop(true);
    this.setResizable(false);

    Toolkit tk = Toolkit.getDefaultToolkit();
    int xsize = (int) tk.getScreenSize().getWidth();
    int ysize = (int) tk.getScreenSize().getHeight();

    this.setSize(xsize, ysize);

    Container1 = new JPanel();  //Initialisation de la grille de Sudoku en JTextField
    Container1.setLayout(null);
    Container1.setBounds((this.getWidth()/2)-(9*60/2),(this.getHeight()/2)-(9*60/2),9*60,9*60);
    Container1.setBackground(Color.white);

    for(int li = 0; li<9; li++){    //Rempli les JTextField avec les nombres dans NOMBRES_DEBUT
        for (int col = 0; col<9; col++){
            //Things here
        }
    }

    // Création des 4 boutons
    int xButton = 170;
    int yButton = (int) ((xButton*3)/4);

    verify.setBounds((xsize/4)-(xButton/2), (ysize/4)-(yButton/2), xButton, 3*yButton/4);
    verify.addActionListener(this);
    verify.setBackground(new Color(50, 150, 251));
    verify.setOpaque(true);
    verify.setBorderPainted(true);

    solve.setBounds((xsize/4)-(xButton/2), (ysize/2)-(yButton/2), xButton, 3*yButton/4);
    solve.addActionListener(this);
    solve.setBackground(new Color(50, 150, 251));
    solve.setOpaque(true);
    solve.setBorderPainted(true);

    reset.setBounds((xsize/4)-(xButton/2), (3*ysize/4)-(yButton/2), xButton, 3*yButton/4);
    reset.addActionListener(this);
    reset.setBackground(new Color(50, 150, 251));
    reset.setOpaque(true);
    reset.setBorderPainted(true);

    submit.setBounds((xsize/2)-(xButton/2), (7*ysize/8)-(yButton/2), xButton, 3*yButton/4);
    submit.addActionListener(this);
    submit.setBackground(new Color(50, 150, 251));
    submit.setOpaque(true);
    submit.setBorderPainted(true);

    containermain = new JPanel();
    containermain.setBounds(0,0, xsize, ysize);
    containermain.setOpaque(false);
    containermain.setLayout(null);

    // Crée et ajoute le fond d'écran au JLabel
    FOND_ECRAN = new JLabel ();
    FOND_ECRAN.setBounds(0, 0, 1920, 1080);
    containermain.add(FOND_ECRAN);
    containermain.add(verify);
    containermain.add(solve);
    containermain.add(reset);
    containermain.add(submit);

    // Récupère l'image de l'ordinateur
    ImageIcon temp = new ImageIcon("C:\\Users\\Maxime\\Documents\\Perso\\Post-Bac\\INSA\\Projet Info\\nature-1520704451453-7117.jpg");
    Image img = temp.getImage();
    ImageIcon imageIcon = new ImageIcon(img);
    FOND_ECRAN.setIcon(imageIcon); // Donne l'image comme fond d'écran

    setContentPane(containermain);

    containermain.add(Container1);

    this.setVisible(true);
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
@Override
public void actionPerformed(ActionEvent e) {
    // Things happen

}

}