如何让子列表引用他原来的ArrayList？

Question

I have a homework to do in java about ArrayList and Generics types.

I have 2 classes : -> CoupeDeA -> TableauPartiel

CoupeDeA is just a describer from where to where an array is cut. (It contains only two private integer variables "begin" and "end")

TableauPartiel is the class where the ArrayList is.

My problem is I need to create a method in TableauPartiel like this :

public TableauPartiel<E> coupe(CoupeDeA coupe)

And the TableauPartiel returned needs to be a reference of my intial TableauPartiel. Example :

Integer[] arr = {8,7,6,5};
TableauPartiel<E> tab = new TableauPartiel<>(arr);

TableauPartiel<E> tab2 = tab.coupe(1,3);
tab2.set(1,45);

This code is supposed to set 45 at index 1 of my tab2 and at the same time set 45 at index 2.

But I tried many different ways and I managed to get the sublist, but it is not pointing to my original ArrayList.

For example, I tried something like this :

private ArrayList<E> tableau;
...
public TableauPartiel<E> coupe(Coupe coupe)
            throws IndexOutOfBoundsException {
    if (coupe.getBegin() >= 0 && coupe.getEnd() <= tableau.size()) {

        TableauPartiel<E> tab = new TableauPartiel<>((E[]) new Object[coupe.getEnd()-coupe.getBegin()]);

        for (int i = 0; i < coupe.getEnd()-coupe.getBegin(); ++i) {
            tab.set(i, this.get(coupe.getBegin()+i));
        }

        return tab;

    } else {
        throw new IndexOutOfBoundsException();
    }
}

How can I do to get a sublist which refers to his original ArrayList?

I've found a solution for my code with the subList method and by switching the signature of my ArrayList to List but my teacher doesn't want us to use subList finally. Here is my code with the subList method :

TableauPartiel<E> tab;

if (coupe.getDebut() >= 0 && coupe.getFin() <= taille()) {
    if (coupe.getFin() == -1)
        tab = new TableauPartiel<>(tableau.subList(coupe.getDebut(),taille()));
    else
        tab = new TableauPartiel<>(tableau.subList(coupe.getDebut(),coupe.getFin()));

     return tab;
    } else {
    throw new IndexOutOfBoundsException();
    }
}

Answer 1

Few small things first:

• stick to English words in your code. Especially in names of classes, functions, variables, etc - names have to reveal intentions (without Google Translate). Best not to obtain a bad habit by letting yourself do otherwise.
• I am not so sure how your Coupe is expected to work (is 0 a legal min number or 1 ?) but coupe.getEnd() <= tableau.size() might get out of hand

Now my suggestion for the solution:

I suggest you modify your TableauPartiel class to have start and end integer fields in addition to private ArrayList<E> tableau; reference you already have. Maybe add a new 'copy constructor' accepting an instance of TableauPartiel (from which you can copy reference to tableau ) and two int values indicating which part of the original tableau you can use (trick here is to also look at start and end values of the object you're 'sublisting' from). That way, when you're calling #coupe you can check for validity of the input numbers (as you already do) and simply return a new TableauPartiel object with a reference to this and method params - start and end values. Add some indexes manipulation logic using those start and end to whatever methods your TableauPartiel has and you should be good to go.