Why does writeObject throw java io NotSerializableException and how do I fix it

Question

I have this exception and I don t understand why it would be thrown or  how I  should handle it   try       os writeObject element     catch  IOException e        e printStackTrace        Where element is a TransformGroup containing some other TransformGroups an instance of the class Atom   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             The full error log   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    AppSetting  in Atom class  is just a custom class that extends Appearance

User · Answer

java io NotSerializableException can occur when you serialize an inner class instance because   serializing such an inner class instance will result in serialization of its associated outer class instance as well Serialization of inner classes  i e   nested classes that are not static member classes   including local and anonymous classes  is strongly discouraged  Ref  The Serializable Interface

User · Answer

Make the class serializable by implementing the interface java io Serializable    java io Serializable - Marker Interface which does not have any methods in it  Purpose of Marker Interface - to tell the ObjectOutputStream that this object is a serializable object

User · Answer

The fields of your object have in turn their fields  some of which do not implement Serializable  In your case the offending class is TransformGroup  How to solve it    if the class is yours  make it Serializable if the class is 3rd party  but you don t need it in the serialized form  mark the field as transient if you need its data and it s third party  consider other means of serialization  like JSON  XML  BSON  MessagePack  etc  where you can get 3rd party objects serialized without modifying their definitions

[java] Why does writeObject throw java.io.NotSerializableException and how do I fix it?

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