This week's book giveaway is in the Cloud/Virtualization forum. We're giving away four copies of Learning OpenStack Networking: Build a solid foundation in virtual networking technologies for OpenStack-based clouds and have James Denton on-line! See this thread for details.
Because an ObjectOutputStream writes a header, too. Take a look at the size of the file that's been written - it's bigger than just the 4 bytes that writeInt() would give you. You really don't want to read this with anything other than an ObjectInputStream. Or in this case, if you're not going to use writeObject() and readObject() at some point, there's really no need to be using the ObjectOutput streams at all.