Testing Object Equality using Serialization

Question

Hey everyone! I was wondering if somebody could help me figure out how to compare two objects using serialization.
I have two objects that I'm trying to compare. Both of these objects extend a common "Model" class that has a method getSerialized() that returns a serialized form of an instance, shown below:
          // Serialize the object to an array
         ByteArrayOutputStream baos = new ByteArrayOutputStream(1000);
         ObjectOutputStream oos;
          try {
               oos = new ObjectOutputStream(baos);
              oos.writeObject(this);
              oos.close();
          } catch (IOException e) {
               e.printStackTrace();
         //Deserialize array into a String array
         return baos.toByteArray();This Model class also has an equals(Model obj) method that allows for the current model object to be compared to a model object that is passed in:
        //Store both models' serialized forms into byte arrays
        byte [] thisClass = this.getSerialized();
        byte [] otherClass = obj.getSerialized();This is where things get a little funny. The byte arrays don't equal - one array is a byte larger than the other. If a byte-by-byte comparison is done, the arrays are equal for the first 15-20% and then not equal for the rest. If I deserialize the byte arrays back into Models and do a toString() on those models, I find that they are equal.
I have a feeling there's something about the serialization process that I don't fully comprehend. Is there a way to properly implement object comparison using serialization?
Thanks in advance!

Answer 1

When you serialize an object, you also serialize the entire tree of references based on that object (except for transient variables). That tree is the complicated business you described there. Serialization stores all the objects in the tree, along with data that explains which objects refer to which other objects. Furthermore if the tree is actually a graph, and there are multiple ways to get to an object, it still only stores each object once. I don't see any reason to believe that all that relationship data would be encoded identically for a pair of trees that you deemed to be equal. And your experiment shows that indeed it isn't.