title: Why does writeObject throw java.io.NotSerializableException and how do I fix it?
body: <p>I have this exception and I don't understand why it would be thrown or, how I  should handle it.</p>
  
  <pre><code>try {
      os.writeObject(element);
  } catch (IOException e) {
      e.printStackTrace();
  }
  </code></pre>
  
  <p>Where <code>element</code> is a <code>TransformGroup</code> containing some other <code>TransformGroups</code> an instance of the class Atom:</p>
  
  <pre><code>public class Atom extends Group implements Serializable{
      float pozX,pozY;
      Group group= new Group();   
      Color3f blue = new Color3f(new Color(255));
      Color3f black = new Color3f(new Color(0));
      Sphere AtSph=new Sphere();
  
      public Atom(final float WEIGHT, final int BOUNDS,final float radius,Color3f color)
      {
          AppSetting ap= new AppSetting(color, black);
          AtSph=new Sphere(radius,1,100,ap);
      }
  }
  </code></pre>
  
  <p>The full error log:</p>
  
  <pre><code>java.io.NotSerializableException: javax.media.j3d.TransformGroup
      at java.io.ObjectOutputStream.writeObject0(Unknown Source)
      at java.io.ObjectOutputStream.writeObject(Unknown Source)
      at cls.MolecularBuilder.addAtom(MolecularBuilder.java:511)
      at cls.MolecularBuilder$Console.HidrogenItemActionPerformed(MolecularBuilder.java:897)
      at cls.MolecularBuilder$Console$2.actionPerformed(MolecularBuilder.java:746)
      at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
      at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
      at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
      at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
      at javax.swing.AbstractButton.doClick(Unknown Source)
      at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
      at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
      at java.awt.Component.processMouseEvent(Unknown Source)
      at javax.swing.JComponent.processMouseEvent(Unknown Source)
      at java.awt.Component.processEvent(Unknown Source)
      at java.awt.Container.processEvent(Unknown Source)
      at java.awt.Component.dispatchEventImpl(Unknown Source)
      at java.awt.Container.dispatchEventImpl(Unknown Source)
      at java.awt.Component.dispatchEvent(Unknown Source)
      at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
      at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
      at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
      at java.awt.Container.dispatchEventImpl(Unknown Source)
      at java.awt.Window.dispatchEventImpl(Unknown Source)
      at java.awt.Component.dispatchEvent(Unknown Source)
      at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
      at java.awt.EventQueue.access$200(Unknown Source)
      at java.awt.EventQueue$3.run(Unknown Source)
      at java.awt.EventQueue$3.run(Unknown Source)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
      at java.awt.EventQueue$4.run(Unknown Source)
      at java.awt.EventQueue$4.run(Unknown Source)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
      at java.awt.EventQueue.dispatchEvent(Unknown Source)
      at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
      at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
      at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
      at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
      at java.awt.EventDispatchThread.run(Unknown Source)
  </code></pre>
  
  <p><code>AppSetting</code> (in Atom class) is just a custom class that extends Appearance.</p>