Question

I have some ArrayLists declared. Some of them are ArrayList<Integer> and other are ArrayList<Double>.

I want to get them from another class, so I wrote a method:

private ArrayList<Double> list1, list2;
private ArrayList<Integer> list3;

    public ArrayList getList(String nameOfList){
        ArrayList myList = new ArrayList();
        if(nameOfList.equals("list1")) myList = list1;
        else if(nameOfList.equals("list2")) myList = list2;
        else if(nameOfList.equals("list3")) myList = list3;
        return myList;
    }

This compiles, but throws me some warnings:

*ArrayList is a raw type. References to generic type ArrayList<E> should be parameterized* in the method above, and *Type safety: The expression of type ArrayList needs unchecked conversion to conform to List<? extends Number>* when calling the method from here:

    XYSeries series = new SimpleXYSeries(data.getList("list1"), data.getList("list2"), "My chart");

where SimpleXYSeries is a chart whose constructor expects to be getting **(List<? extends Number>, List<? extends Number>, String)**.

Which is the right way to do what I’m intending to do?

Answer 1

Use multiple methods instead of one god method.

This is poor design to have one getList method that uses a String to select a member. Instead, there should be multiple methods – one for each list. Then each method can return the type appropriate to its list.