Trying to do something very strange with layouts and painting components

Question

I'm trying to do something very strange with changing the layout of a container, then painting it to a bufferedImage and changing it back again so nothing has changed. However, I am unable to get the image i want of this container in a new layout. Consider it a preview function of the different layouts. Anyway. I've tried everything i know about swing and have come up empty. There is probably a better way to do what i am trying to do, i just don't know how.
If someone could have a look perhaps and help me out i would be much appreciative.
Here is a self contained small demo of my conundrum.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import javax.swing.BoxLayout;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.LineBorder;
// what is should do is when you click on the button "click me" it should place a image on the panel of the buttons in a
// horizontal fashion. Instead it shows the size that the image should be, but there is no image.
public class ChangeLayoutAndPaint
     private static JPanel panel;
     private static JLabel label;
     public static void main(String[] args)
          // the panel spread out vertically
          panel = new JPanel();
          panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
          // the buttons in the panel
          JButton b1, b2, b3;
          panel.add(b1 = new JButton("One"));
          panel.add(b2 = new JButton("Two"));
          panel.add(b3 = new JButton("Three"));
          b1.setEnabled(false);
          b2.setEnabled(false);
          b3.setEnabled(false);
          // the label with a border around it to show size in a temp panel with flowlayout to not stuff around
          // with the actual size we want.
          JPanel thingy = new JPanel();
          label = new JLabel();
          label.setBorder(new LineBorder(Color.black));
          thingy.add(label);
          // the button to make things go
          JButton button = new JButton("click me");
          button.addActionListener(new ActionListener(){
               public void actionPerformed(ActionEvent e)
                    //change layout
                    panel.setLayout(new BoxLayout(panel, BoxLayout.X_AXIS));
                    panel.doLayout();
                    //get image
                    BufferedImage image = new BufferedImage(panel.getPreferredSize().width, panel.getPreferredSize().height, BufferedImage.TYPE_INT_ARGB);
                    Graphics2D g = image.createGraphics();
                    panel.paintComponents(g);
                    g.dispose();
                    //set icon of jlabel
                    label.setIcon(new ImageIcon(image));
                    //change back
                    panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
                    panel.doLayout();
          // the frame
          JFrame frame = new JFrame();
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.setSize(400,200);
          frame.setLocation(100,100);
          frame.getContentPane().add(panel, BorderLayout.NORTH);
          frame.getContentPane().add(thingy, BorderLayout.CENTER);
          frame.getContentPane().add(button, BorderLayout.SOUTH);
          frame.setVisible(true);
}

Answer 1

Looks like you didn't read the API for Container#doLayout().
Causes this container to lay out its components. Most programs should not call this method directly, but should invoke the validate method instead.
There's also a concurrency issue here in that the panel's components may be painted to the image before revalidation completes. And your GUI, like any Swing GUI, should be constructed and shown on the EDT.
Try this for size -- it could be better, but I've made the minimum possible changes in your code:import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import javax.swing.BoxLayout;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.border.LineBorder;
public class ChangeLayoutAndPaint {
  private static JPanel panel;
  private static JLabel label;
  public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
      @Override
      public void run() {
        // the panel spread out vertically
        panel = new JPanel();
        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
        // the buttons in the panel
        JButton b1, b2, b3;
        panel.add(b1 = new JButton("One"));
        panel.add(b2 = new JButton("Two"));
        panel.add(b3 = new JButton("Three"));
        b1.setEnabled(false);
        b2.setEnabled(false);
        b3.setEnabled(false);
        // the label with a border around it to show size in a temp panel with flowlayout to not stuff around
        // with the actual size we want.
        JPanel thingy = new JPanel();
        label = new JLabel();
        // label.setBorder(new LineBorder(Color.black));
        thingy.add(label);
        // the button to make things go
        JButton button = new JButton("click me");
        button.addActionListener(new ActionListener() {
          @Override
          public void actionPerformed(ActionEvent e) {
            //change layout
            panel.setLayout(new BoxLayout(panel, BoxLayout.X_AXIS));
            //panel.doLayout();
            panel.revalidate();
            SwingUtilities.invokeLater(new Runnable() {
              @Override
              public void run() {
                //get image
                BufferedImage image = new BufferedImage(panel.getPreferredSize().width,
                    panel.getPreferredSize().height, BufferedImage.TYPE_INT_ARGB);
                Graphics2D g = image.createGraphics();
                panel.paintComponents(g);
                g.dispose();
                //set icon of jlabel
                label.setIcon(new ImageIcon(image));
                //change back
                panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
                //panel.doLayout();
                panel.revalidate();
        // the frame
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 200);
        frame.setLocation(100, 100);
        frame.getContentPane().add(panel, BorderLayout.NORTH);
        frame.getContentPane().add(thingy, BorderLayout.CENTER);
        frame.getContentPane().add(button, BorderLayout.SOUTH);
        frame.setVisible(true);
}db
edit I prefer this:import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import javax.swing.*;
public class LayoutAndPaint {
  JPanel panel;
  JLabel label;
  public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
      @Override
      public void run() {
        new LayoutAndPaint().makeUI();
  public void makeUI() {
    JButton one = new JButton("One");
    JButton two = new JButton("Two");
    JButton three = new JButton("Three");
    one.setEnabled(false);
    two.setEnabled(false);
    three.setEnabled(false);
    panel = new JPanel();
    panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
    panel.add(one);
    panel.add(two);
    panel.add(three);
    label = new JLabel();
    JButton button = new JButton("Click");
    button.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(ActionEvent e) {
        layoutAndPaint();
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 400);
    frame.add(panel, BorderLayout.NORTH);
    frame.add(label, BorderLayout.CENTER);
    frame.add(button, BorderLayout.SOUTH);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  private void layoutAndPaint() {
    panel.setLayout(new BoxLayout(panel, BoxLayout.X_AXIS));
    panel.revalidate();
    SwingUtilities.invokeLater(new Runnable() {
      @Override
      public void run() {
        BufferedImage image = new BufferedImage(panel.getPreferredSize().width,
            panel.getPreferredSize().height, BufferedImage.TYPE_INT_ARGB);
        Graphics g = image.createGraphics();
        panel.paintComponents(g);
        g.dispose();
        label.setIcon(new ImageIcon(image));
        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
        panel.revalidate();
}db
Edited by: DarrylBurke