Arraylist of two types that implement java.io.Serializable

Question

For example I have:

    public class Class1 implements Serializable {
       private static final long serialVersionUID = 1L;
       private int a;
       private int b;

       /*Getters and setters here*/
       public int getA();
    }

    public class Class2 implements Serializable {
       private static final long serialVersionUID = 1L;
       private int a;
       private int b;

       /*Getters and setters here*/
       public int getA();
    }

Now I want to make an ArrayList of those two types. This is what I'm trying:

List<Serializable> list= new ArrayList<Serializable>();

I have a method that returns Serializable, which returns the object in the list:

  public Serializable get(int i)
{
    return list.get(i);
}

However, when I'm trying to use the getter method from the two classes above( something like list.get(0).getA()) , there's an error saying the getA() method is not defined for Serializable. Am I missing something simple here? What should I use for the return type of the method above in order to use the getter method? Thanks.

Answer 1

You are returning a Serializable object, not a Class1 object. There are two routes to doing this, but I recommend the latter:

Serializable s = list.get(1);
if (s instanceof Class1) {
    Class1 clazz = (Class1) s;
    clazz.getA();
} //etc...

Or, using a common interface:

public interface YourClass extends Serializable {

    public int getA();

}

//...

List<YourClass> list = new ArrayList<>();