Null pointer exception in embedded component

Question

Hi all,
I am trying to build a custom component that serves as a container. Unfortunately I consistently hit a null pointer exception in javax.swing.BufferStrategyPaintManager.flushAccumulatedRegion when my custom component contains a JPanel.
You'll find below the smallest code that reproduces the problem and the exception that comes with it.
In my testing I noticed few things:
- If the contained object is simple (a JButton for example), there is no problem.
- When I turn off double buffering, there is no problem.
- I figured out that I need to set the contained component size and its internal components to have it display properly.
I can't figure out what would make this work.
I'm using JDK 6.
package test;
import java.awt.*;
import javax.swing.*;
public class Test {
     public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
     private static void createAndShowGUI() {
          // internal panel
          JPanel lPanel = new JPanel();
          JButton lButton = new JButton("Button 1");
          lButton.setSize(lButton.getPreferredSize());
          lPanel.add(lButton);
          IntComponent b = new IntComponent(lPanel);
          JFrame lFrame = new JFrame("internal panel test");
          //RepaintManager.currentManager(null).setDoubleBufferingEnabled(false);
          lFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          lFrame.getContentPane().add(b);
          lFrame.pack();
          lFrame.setVisible(true);
class IntComponent extends JComponent {
     private JComponent mInternalComponent;
     public IntComponent(JComponent iComponent) {
          mInternalComponent=iComponent;
          mInternalComponent.setSize(mInternalComponent.getPreferredSize());
     public Dimension getMaximumSize() {
          return getPreferredSize();
     public Dimension getMinimumSize() {
          return getPreferredSize();
     public Dimension getPreferredSize() {
          return mInternalComponent.getPreferredSize();
     protected void paintComponent(Graphics g) {
          mInternalComponent.paint(g);
}Exception:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
     at javax.swing.BufferStrategyPaintManager.flushAccumulatedRegion(BufferStrategyPaintManager.java:406)
     at javax.swing.BufferStrategyPaintManager.endPaint(BufferStrategyPaintManager.java:370)
     at javax.swing.RepaintManager.endPaint(RepaintManager.java:1192)
     at javax.swing.JComponent.paint(JComponent.java:1016)
     at java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:21)
     at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:60)
     at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:97)
     at java.awt.Container.paint(Container.java:1797)
     at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:734)
     at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:679)
     at javax.swing.RepaintManager.seqPaintDirtyRegions(RepaintManager.java:659)
     at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:128)
     at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
     at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
     at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
     at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
     at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
     at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
     at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

Answer 1

import java.awt.*;
import javax.swing.*;
class Test {
  public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
  private static void createAndShowGUI() {
    JPanel lPanel = new JPanel();
    JButton lButton = new JButton("Button 1");
    lPanel.add(lButton);
    IntComponent b = new IntComponent(lPanel);
    JFrame lFrame = new JFrame("internal panel test");
    lFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    lFrame.getContentPane().add(b);
    lFrame.pack();
    lFrame.setVisible(true);
class IntComponent extends JComponent {
  private JComponent mInternalComponent;
  public IntComponent(JComponent iComponent) {
    mInternalComponent=iComponent;
    setLayout(new FlowLayout());//<--added
    add(mInternalComponent);//<--added
  public Dimension getMaximumSize() {
    return getPreferredSize();
  public Dimension getMinimumSize() {
    return getPreferredSize();
  public Dimension getPreferredSize() {
    return mInternalComponent.getPreferredSize();
  protected void paintComponent(Graphics g) {
    //mInternalComponent.paint(g);//<--error from this
    super.paintComponent(g);//<---added
}