Java Swing - Show multiple panels

Question

I'm using the Java Swing UI Designer in IntelliJ :( I designed something in the designer using multiple panels and spacers with 1 parent panel. When I add the main panel, the first one inside it shows, but the others don't.

Frame structure:

• Panel1
  • GradientPanel
    • Panel
    • Spacers

What I designed

What I get

import keeptoo.KGradientPanel;

import javax.swing.*;

public class LogIn extends JFrame{
private KGradientPanel KGradientPanel1; //Automatically added by the designer
private JPanel panel1; //Automatically added by the designer

public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setTitle("CarbonTec Dashboard");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setResizable(false);
    frame.setSize(1800,1000);
    frame.setContentPane(new LogIn().panel1);
    frame.setVisible(true);

    ImageIcon imageIcon = new ImageIcon("Icon.png");
    frame.setIconImage(imageIcon.getImage());
}
}

Answer 1

First you need to know that your class is a JFrame, but in the main method you create a new JFrame.

Better would be to have a class Program that has the main method. In this main method you make a new instance of LogIn.

The Program class can look like this:

public class MainProgram {

  public static void main(String[] args) {
    LogIn logIn = new LogIn();
  }
}

The LogIn class should then look like this:

    import keeptoo.KGradientPanel;
    import javax.swing.*;

    public class LogIn extends JFrame{
    private KGradientPanel KGradientPanel1 = new KGradientPanel(); //Automatically added by the designer
    private JPanel panel1 = new JPanel(); //Automatically added by the designer
    

    // This is the constructor.
    public LogIn {
    
        setTitle("CarbonTec Dashboard");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setResizable(false);
        setSize(1800,1000);
        setContentPane(panel1);
    
        ImageIcon imageIcon = new ImageIcon("Icon.png");
        setIconImage(imageIcon.getImage());

        // Here you can add the gradient panel to panel1.
        panel1.add(KGradientPanel1); // The name should be written in lower case.
       
        setVisible(true);
    }

But I don't know why you need the panel1, you could add the KGradientPanel directly.