The above code is untested but should work.

You only need to declare the attributes type and my_id in theparent class ALL. A child class is an extension of the parent class and as such will automatically include the parent's attributes. Redefining them in the child is dangerous because you end up with multiple attributes with the same name.

Also when you create a child object e.g.

1. new B();

it will execute the parent class constructor i.e. super() THEN it will execute the child class constructor.

Just realised I can optimise it a little more:

2. class ALL{
3.       String type;
4.       int my_id;
5. 
   
6.       ALL(){ 
7.             type = "Basic";
8.             my_id = current_id++;
9.             array[my_id] = this;
10.       }
11. }
12. 
    
13. class A extends ALL{
14.       A(){         
15.             type = "B type";
16.       }
17. }
18. 
    
19. class B extends ALL{
20.       B(){ 
21.             type = "B type";
22.       }
23. }
25. 
    

Can I ask what the "super()" is used for?