Java proper extension design for a class with a generic collection

Question

Let's say I got classes A,B,C such that B extends A and C also extends A.

Now I got 2 different classes, lets call them MyClassB and MyClassC with a member of ArrayList<B> and ArrayList<C> respectfuly.

Since many actions in MyClassB and MyClassC are the same and are only done on the different type of ArrayList, I wanted to create a new abstract class MyClassA which will have an implementation of the same actions on an ArrayList<A> for both classe, since A is the common part which the actions are the same on.

So I tried creating a method in the new MyClassA class which receives a list as an argument and is supposed to make the action on that list. However, I can't pass an ArrayList<B> to the method where it expects ArrayList<A>.

So what can I do in order to keep the same actions in a different class and not repeat the code in 2 different classes?

Answer 1

class MyClassA<T extends A>
{
    ArrayList<T> list;

    public MyClassA(ArrayList<T> list)
    {
        this.list = list;

...

class MyClassB extends MyClassA<B>
{
    MyClassB(ArrayList<B> list)
    {
         super(list);

Answer 2

Try with generics:

public class MyClassA<T extends A> {
    public void doSomething(ArrayList<T> list) {
        // do something
    }
}

Now MyClassB and MyClassC can inherit from it and you can work with the list normally.