Re: NotSerializableException

Robert Klemme <>
Tue, 14 Apr 2015 07:50:53 +0200
On 14.04.2015 03:51, wrote:


My code is as follows:

         File ser = new File("locationinstringform");
         FileInputStream fileIn3 = new FileInputStream(ser);
         ObjectInputStream objectIn3 = new ObjectInputStream(fileIn3);
         myObj = (MyObj) objectIn3.readObject();
         myObj.someFunction(x, y);
         FileOutputStream fileOut3 = new FileOutputStream(ser);
         ObjectOutputStream objectOut3 = new ObjectOutputStream(fileOut3);

When I run my code, I get an error tracing to the line that says objectOut3.writeObject(myObj);

The error is as follows:
Exception in thread "main" java.util.HashMap$KeySet

However, that MyObj class I have defined isn't a HashMap or Set, and
doesn't have a HashMap or Set. It only has 2 instance objects, one of
which is one is an object I coded, and the other is an ArrayList. I
have made sure all classes I have coded implement the serializable

Obviously that assumption must be false: there must be a HashMap or sub
class of it somewhere in the graph of objects you are trying to
serialize. Since you seem to read it from a serialized stream
candidates to look closer are someFunction() as well as readResolve(),
readObject() and readObjectNoData() and their write counterparts. See

Any ideas as to why the problem could be arising and what the
solution is? I have been stuck for a long time so any help would be
much appreciated.

Without seeing class MyObj and probably also super and sub classes it's
all only guessing.



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