Automatically Size Jpanel Inside Jframe

Automatically size JPanel inside JFrame

You can set a layout manager like BorderLayout and then define more specifically, where your panel should go:

MainPanel mainPanel = new MainPanel();
JFrame mainFrame = new JFrame();
mainFrame.setLayout(new BorderLayout());
mainFrame.add(mainPanel, BorderLayout.CENTER);
mainFrame.pack();
mainFrame.setVisible(true);

This puts the panel into the center area of the frame and lets it grow automatically when resizing the frame.

how to do auto-resizing drawings in JPanel?

Provide positions and sizes as a proportion of the width and height of the panel. Whenever the panel is resized, the rendering engine will schedule a call to the paintComponent() method and the rectangle will be drawn proportionally. E.G.

import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.*;

public class DrawRect extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        int w = getWidth();
        int h = getHeight();
        g.drawRect(w/10, h/10, w/2, h/2);
    }

    /* A custom component should give the layout manager hints as to
    its preferred size. */
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(200,200);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        DrawRect panel = new DrawRect();

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(panel);
        frame.pack();
        frame.setVisible(true);
    }
}

How to set JPanel height to auto

I use JScrollPane to make JFrame scrollable so the entire form is visible.

package helpdesk;

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

/**
 *
 * @author Joko Wandiro
 */
public class Layout extends Base {

    JPanel panel_form_edit = new JPanel();
    FlowLayout layout_form_edit_outer = new FlowLayout(FlowLayout.LEFT);
    JPanel panel_form_edit_outer = new JPanel();
    // Form - Edit
    JLabel label_name_update = new JLabel("Name", JLabel.LEFT);
    JTextField input_id_update = new JTextField();
    JTextField input_name_update = new JTextField();
    JButton btn_update = new JButton("Update");

    public Layout() {
        setLookAndFeel();
        setExtendedState(JFrame.MAXIMIZED_BOTH);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // Main Layout
        GridLayout layout = new GridLayout(5, 1, 10, 10);
        setLayout(layout);
        // Form - Edit
        label_name_update.setPreferredSize(new Dimension(400, 20));
        input_name_update.setPreferredSize(new Dimension(400, 20));
        input_id_update.setVisible(false);
        GridLayout layout_form_edit = new GridLayout(4, 1, 10, 10);
        panel_form_edit.setLayout(layout_form_edit);
        panel_form_edit.add(input_id_update);
        panel_form_edit.add(label_name_update);
        panel_form_edit.add(input_name_update);
        panel_form_edit.add(btn_update);
        panel_form_edit_outer.setLayout(layout_form_edit_outer);
        panel_form_edit_outer.add(panel_form_edit);
        add(panel_form_edit_outer);
        // Set window or jframe scrollable
        Container container = getContentPane();
        JScrollPane scroll = new JScrollPane(container);
        setContentPane(scroll);
        setVisible(true);
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        Layout app = new Layout();
    }

    private void setLookAndFeel() {
        try {
            UIManager.setLookAndFeel(
                    "com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel"
            );
        } catch (Exception exc) {
            // ignore error
        }
    }

}

controlling JPanels size according to JFrame Resize

You must test this code:

if (jpanelDarkGray.getHeight() != jpanelLightGray.getHeight()) {
  if (jpanelMidSep.getHeight() == 8) {
    jpanelMidSep.setPreferredSize(new Dimension(jpanelMidSep.getWidth(), 9));
  }
  if (jpanelMidSep.getHeight() == 9) {
    jpanelMidSep.setPreferredSize(new Dimension(jpanelMidSep.getWidth(), 8));
  }
}

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