Serialize multiple different objects single in Java

Question

I might be trying to do this the hard way so let me know if there is a better solution.

I am making a simple text game in Java which you select your actions by a GUI. I have a couple of classes I am trying to serialize one being the player and another being an NPC. Is there an easy way to serialize more then one object (player and NPC) into the same file? I can serialize one object and load it back into the game.

Am I going about this the wrong way? Is there a simpler way of trying to save the game state?

If I have a class that creates multiple objects and I serialize that class, will the objects it created be serialized as well?

Thanks

Answer 1

An alternate approach to writing objects sequentially is to store them in a collection (e.g. a HashMap), since collections can be serialized. This may make it a little easier to manage upon retrieval, especially if you have many objects to serialize/deserialize. The following code demonstrates this:

 String first = "first";
 String second = "second";
 HashMap<String, Object> saved = new HashMap<String, Object>();
 saved.put("A", first);
 saved.put("B", second);
 try {
 FileOutputStream fos = new FileOutputStream("test.obj");
 ObjectOutputStream oos = new ObjectOutputStream(fos);
 oos.writeObject(saved);
 oos.flush();
 oos.close();
 fos.close();
 FileInputStream fis = new FileInputStream("test.obj");
 ObjectInputStream ois = new ObjectInputStream(fis);
 HashMap<String,Object> retreived = (HashMap<String,Object>)ois.readObject();
 fis.close();
 System.out.println(retreived.get("A"));
 System.out.println(retreived.get("B"));
 } catch (IOException e) {
 e.printStackTrace();
 } catch (ClassNotFoundException e) {
 e.printStackTrace();
 }
}

Running this should result in:

first
second

• jprogrammer: Thanks, this looks like it has worked. Instead of just printing out "A" and "B" into the console how as assign it back to an object I can do things with?
• jprogrammer: I figured it out from here: stackoverflow.com/questions/7857935/… Thanks again for your answer it put me on the right track :)

Answer 2

Just call writeObject() as many times with as many different objects as you need, and conversely call readObject() ditto.

Hard to believe you haven't already tried it.