Question

I’m doing a little homework on Java, but I’m not good at it and I’m having issues trying to use XMLEncoder to store an App objects to a file.

In short my App has and abstract class called animal and another ones that extend the previous one called dogand cat. In my main App I’ve a static method to create new animals that adds the new animal object to a static ArrayList of type animal: public static ArrayList<animal> animalArray = new ArrayList<animal>();

Creating an animal at
kingdom.java:

private static void newAnimal(ArrayList<animal> animalArray) {
            System.out.print("  Enter a name for the dog > ");
            animalArray.add(new dog(keyboard.nextLine()));
            System.out.println("  New dog with name " + animalArray.get(animalArray.size()-1).getName() + ".\n");

            try {
                FileOutputStream afos = new FileOutputStream("animals.xml");
                XMLEncoder encoder = new XMLEncoder(afos);
                encoder.writeObject(animalArray.get(animalArray.size()-1));
                encoder.close();
            } catch(IOException ioe){
                System.out.print("[ERROR!]");
            }
}

My abstract animal class:
animal.java:

public abstract class animal {

    private static int alloc = 0;
    protected int id;
    private String name;

    animal() {
        alloc++;
        id = alloc;
    }

    public void play() {
        System.out.print("   The animal (" + this.id + ") " + this.name + " is now playing... ");
    }

    public void setName(String lname) {
        this.name = lname;
    }

    public String getName() {
        return this.name;
    }

    public static int countAnimals() {
        return alloc;
    }

}

Now, my dog class:
dog.java:

public class dog extends animal {

    dog(String theName) {
        this.setName(theName);
    }

    @Override
    public void play() {
        super.play();
        System.out.println(" Dog Stuff!");
    }

}

When I try to run the code I get:

java.lang.InstantiationException: dog
Continuing ...
java.lang.Exception: XMLEncoder: discarding statement XMLEncoder.writeObject(dog);
Continuing ...

What am I missing? Thank you 😉

Answer 1

You should use as following:

encoder.writeObject(animalArray.get(animalArray.size()-1).getName());

The Dog object itself can’t be saved into XMLEncoder.

Thx.