android - java.io.invalidClassException during serializing/deserializing

Question

I've got an object that im reading and writing to and from fileinputstreams/objectinputstreams and objectinputstreams/objectoutputstreams. I keep getting errors that java excpected one serialversionUID, but found another.

In my class I've implemented serializable and have a field like static final long serialVersionUID = 1L; which I thought was enough.

I'm new to java serialization. What am I missing here?

EDIT If it matters, I'm actually trying to write and read an **ArrayList<MyObject>**

Here's the full trace:

java.io.InvalidClassException: com.luxurymode.pojos.Reminder; Incompatible class (SUID): com.luxurymode.pojos.Reminder: static final long serialVersionUID =4209360273818925922L; but expected com.luxurymode.pojos.Reminder: static final long serialVersionUID =1L;
W/System.err( 4504):    at java.io.ObjectInputStream.verifyAndInit(ObjectInputStream.java:2723)
W/System.err( 4504):    at java.io.ObjectInputStream.readNewClassDesc(ObjectInputStream.java:1848)
W/System.err( 4504):    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:826)
W/System.err( 4504):    at java.io.ObjectInputStream.readNewObject(ObjectInputStream.java:2066)
W/System.err( 4504):    at java.io.ObjectInputStream.readNonPrimitiveContent(ObjectInputStream.java:929)
W/System.err( 4504):    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:2285)
W/System.err( 4504):    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:2240)
W/System.err( 4504):    at java.util.ArrayList.readObject(ArrayList.java:662)
W/System.err( 4504):    at java.lang.reflect.Method.invokeNative(Native Method)
W/System.err( 4504):    at java.lang.reflect.Method.invoke(Method.java:521)
W/System.err( 4504):    at java.io.ObjectInputStream.readObjectForClass(ObjectInputStream.java:1537)
W/System.err( 4504):    at java.io.ObjectInputStream.readHierarchy(ObjectInputStream.java:1460)
W/System.err( 4504):    at java.io.ObjectInputStream.readNewObject(ObjectInputStream.java:2139)
W/System.err( 4504):    at java.io.ObjectInputStream.readNonPrimitiveContent(ObjectInputStream.java:929)
W/System.err( 4504):    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:2285)
W/System.err( 4504):    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:2240)
W/System.err( 4504):    at com.luxurymode.singletons.RemindersSingleton.<init>(RemindersSingleton.java:54)
W/System.err( 4504):    at com.luxurymode.singletons.RemindersSingleton.getInstance(RemindersSingleton.java:66)
W/System.err( 4504):    at com.luxurymode.views.AddReminderView.saveAlarm(AddReminderView.java:290)
W/System.err( 4504):    at com.luxurymode.tab_2.RemindersActivity.onClick(RemindersActivity.java:94)
W/System.err( 4504):    at android.view.View.performClick(View.java:2554)
W/System.err( 4504):    at android.view.View$PerformClick.run(View.java:8962)
W/System.err( 4504):    at android.os.Handler.handleCallback(Handler.java:587)
W/System.err( 4504):    at android.os.Handler.dispatchMessage(Handler.java:92)
W/System.err( 4504):    at android.os.Looper.loop(Looper.java:123)
W/System.err( 4504):    at android.app.ActivityThread.main(ActivityThread.java:4627)
W/System.err( 4504):    at java.lang.reflect.Method.invokeNative(Native Method)
W/System.err( 4504):    at java.lang.reflect.Method.invoke(Method.java:521)
W/System.err( 4504):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
W/System.err( 4504):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
W/System.err( 4504):    at dalvik.system.NativeStart.main(Native Method)
D/AndroidRuntime( 4504): Shutting down VM

Answer 1

Are you reading from a file? In that case, it does not matter if you added the serialVersionUID now, it is different from the one stored in the file, and that creates the exception.

A quick solution could be to set serialVersionUID to 4209360273818925922L, which seems to be the serialVersionUID that was automatically generated by java when you saved those object in that file at that time :)