ArrayList Serialization with Multiple Instances/Extends

Question

Lets say I have an ArrayList that contains instances of multiple classes that extends from the "People"(Lets call it that) class.

An example: Example two Strings are Name and Course Name

ArrayList<People> people = new ArrayList<>();
people.add(new Teacher("Mrs. Doe","Math"));
people.add(new Student("Bob","Math"));
people.add(new Student("Sue","Math"));
people.add(new Student("Joe","Math"));

Quick example of the structure of these classes:

 abstract class People implements Serializable
    {
        String name;
        String course;
        ...
        private People(String newName, String newCourse)
        {
            this.name = newName;
            ...
        }
        @Override
        public String toString(){return...}
    }
    public class Teacher extends People
    {
        public class Teacher... yada-yada{
        super(variables)}
        @Override String toString(){return...}...
    }
    public class Student extends People
    {
        public class Teacher... yada-yada{
        super(variables)}
        @Override String toString(){return...}...
    }

Is it possible to output the ArrayList to a file without getting any errors(hehe)?

Error: java.io.NotSerializableException: mvc.Model

It yells at me for this line: out.writeObject(people);

Is that not allowed? Is life not this easy? Could these extra instances be interfering with this? I've done some quick dirty code with making a new list without any extra instances and it worked.

Thanks in advanced!

Answer 1

Have you tried writing the array list without the toString. You could serialize the class, then write the ArrayList, just as you would write any other object.

Writing the ArrayList:

    FileOutputStream fos = new FileOutputStream(filename);
    ObjectOutputStream oos = new ObjectOutputStream(fos);
    oos.writeObject(ARRAY_NAME);

Just remember to include the following to decode the serialization:

private static final long serialVersionUID = 123456;

Reading the ArrayList: When trying to read the ArrayList back in, you could do this: (as long as it is from the same serialized class)

    FileInputStream fis = new FileInputStream(filename);
    ObjectInputStream ois = new ObjectInputStream(fis);
    ARRAY_NAME = (ARRAY_TYPE_CAST)ois.readObject();

Answer 2

Is it possible to output the ArrayList to a file without getting any errors(hehe)?

Extend Arraylist and implement java.io.Serializable like this -

public class MyList extends ArrayList implements java.io.Serializable

For you to serialize an object you need to extend java.io.Serializable. Since you need to serialize ArrayList, simply extend it.

PS - Keeping your question simple would get you more help.