Why my frame is invisible every time I call it from the JButton?

Question

I'm creating a Loading Page for our group project, but every time I call the loading page class, it is invisible.

Here is my Main class:

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

Here is the button that when you click you will go into the loading page class.

JFrame frame = new JFrame();
JButton btn = new JButton("Press me!");

caller(){
    
    btn.setBounds(20, 30, 120, 50);
    btn.setFocusable(false);
    btn.addActionListener(this);
    
    
    
    frame.setSize(420, 420);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
    frame.setLayout(null);
    frame.add(btn);
    
}
@Override
public void actionPerformed(ActionEvent e) {
    
    if(e.getSource()==btn) {
        
        frame.dispose();
        new loading_page();
        
        
    }
}

And here is the loading page class

 JLabel lablab = new JLabel();
 JProgressBar bar = new JProgressBar();
 JFrame frame = new JFrame();

loading_page(){
    
    lablab.setBackground(Color.WHITE);
    lablab.setHorizontalAlignment(SwingConstants.CENTER);
    lablab.setIcon(new ImageIcon("C:\\Users\\KHAdmin\\Documents\\Pictures\\giphy.gif"));
    lablab.setBounds(65, 40, 367, 215);
    
    bar.setForeground(Color.cyan);
    bar.setBounds(10, 300, 480, 17);
    bar.setValue(0);
    bar.setStringPainted(true);
    bar.setFont(new Font("MV Boli", Font.BOLD, 15));
    bar.setForeground(Color.CYAN);
    bar.setBackground(Color.BLACK);
    
    frame.setUndecorated(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setBounds(400, 200, 500, 335);
    frame.setVisible(true);
    frame.setLayout(null);
    
    frame.getContentPane().setBackground(Color.BLACK);
    frame.getContentPane().add(lablab);
    frame.getContentPane().add(bar);
    
    
    int counter =0;
    
    while(counter<=100) {
        
        bar.setValue(counter);
        try {
            Thread.sleep(50);
            if(counter==100) {
                frame.dispose();
            }
        } catch (InterruptedException e) {
            
            e.printStackTrace();
        }
        counter +=1;
    
}
    {
        new caller();
    }
}

I think it's in the while(counter<==100) statement. I used the frame dispose to dispose the frame from the previous class, but when the system call the 3rd class which is the loading page class, it's invisible.