writing a BitSet to a file in java

Question

I have a BitSet and want to write it to a file- I came across a solution to use a ObjectOutputStream using the writeObject method.

I looked at the ObjectOutputStream in the java API and saw that you can write other things (byte, int, short etc)

I tried to check out the class so I tried to write a byte to a file using the following code but the result gives me a file with 7 bytes instead of 1 byte

my question is what are the first 6 bytes in the file? why are they there?

my question is relevant to a BitSet because i don't want to start writing lots of data to a file and realize I have random bytes inserted in the file without knowing what they are.

here is the code:

    byte[] bt = new byte[]{'A'};
    File outFile = new File("testOut.txt");
    FileOutputStream fos = new FileOutputStream(outFile);
    ObjectOutputStream oos = new ObjectOutputStream(fos);
    oos.write(bt);
    oos.close();

thanks for any help

Avner

Answer 1

The other bytes will be type information.

Basically ObjectOutputStream is a class used to write Serializable objects to some destination (usually a file). It makes more sense if you think about InputObjectStream. It has a readObject() method on it. How does Java know what Object to instantiate? Easy: there is type information in there.