Not able to add 3 JPanels to a main panel

Question

I have 3 JPanels and I want to place them all in one JPanel. I used the GridBagLayout for the main panel. But only one panel is getting added. Why might this be?

Answer 1

you have to read How to Use GridBagLayout, examples for that here and GridBagConstraints, change your gbc.fill=GridBagConstraints.HORIZONTAL;, if you have problem(s) with JComponent's Size then add setPreferedSize(); for example

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.*;

public class GBLFillBoth extends JFrame {
    private static final long serialVersionUID = 1L;

  public GBLFillBoth() {
    JPanel panel = new JPanel();
    GridBagLayout gbag = new GridBagLayout();
    panel.setLayout(gbag);
    GridBagConstraints c = new GridBagConstraints();
    JButton btn1 = new JButton("One");
    c.fill = GridBagConstraints.BOTH;
    //c.fill = GridBagConstraints.HORIZONTAL;
    c.anchor=GridBagConstraints.NORTHWEST;
    c.gridx = 0;
    c.gridy = 0;
    c.weightx = 0.5;
    c.weighty = 0.5;
    panel.add(btn1, c);
    JButton btn2 = new JButton("Two");
    c.gridx++;
    panel.add(btn2, c);
    //c.fill = GridBagConstraints.BOTH;
    JButton btn3 = new JButton("Three");
    c.gridx = 0;
    c.gridy++;
    c.gridwidth = 2;
    panel.add(btn3, c);
    add(panel);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    pack();
    setVisible(true);
  }

  public static void main(String[] args) {
        GBLFillBoth gBLFillBoth = new GBLFillBoth();
  }
}