i am working on a java project and i want in the begging of the programme to load the things from the file and then add some things... I am getting this error

Code:
"java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException:      pcshop.Pc 

at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
at java.util.ArrayList.readObject(ArrayList.java:733)
...