[JAVA] Metodo ObjectOutputStream.writeObject() ed errore "NotSerializableException"

[acqualol]

Innanzitutto grazie per l'interessamento. Ecco lo stacktrace:

java.io.NotSerializableException: SalvaOggetti
	at java.io.ObjectOutputStream.writeObject0(Unknown Source)
	at java.io.ObjectOutputStream.defaultWriteFields(Unknown Source)
	at java.io.ObjectOutputStream.writeSerialData(Unknown Source)
	at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source)
	at java.io.ObjectOutputStream.writeObject0(Unknown Source)
	at java.io.ObjectOutputStream.writeObject(Unknown Source)
	at java.util.HashMap.writeObject(Unknown Source)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at java.io.ObjectStreamClass.invokeWriteObject(Unknown Source)
	at java.io.ObjectOutputStream.writeSerialData(Unknown Source)
	at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source)
	at java.io.ObjectOutputStream.writeObject0(Unknown Source)
	at java.io.ObjectOutputStream.writeObject(Unknown Source)
	at SalvaOggetti.<init>(SalvaOggetti.java:33)
	at SalvaOggetti.main(SalvaOggetti.java:42)