Converting to int, float, or double from a String

Question

I have a custom MyArrayList that only stores int, float, or double values. I need to add user input to this array list. The input is stored as a string in a temporary variable, and I want to convert this string to the appropriate type before adding it to the list. How can I achieve this?

class MyArrayList<E> extends ArrayList<E>{

    @Override
    public boolean add(E e) {
        if(e instanceof Integer || e instanceof Float || e instanceof Double) {
            super.add(e);
            return true;
        } else {
            throw new ClassCastException("Please enter Integer, Float or Double");
        }
    }
}

public class TestArrayList{
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        MyArrayList<Object> arraylist = new MyArrayList<>();
        Object object = new Object();
        try {
            System.out.println("Enter Elements");
            System.out.println("To stop input press '.'");
            String temp;
            while(scanner.hasNext()) {
                temp = scanner.nextLine();
                try {                   
                    object = temp;
                } catch(Exception e) {}
                if(temp.equals(".")) break;
                else
                    arraylist.add(temp);
            }
            scanner.close();
            System.out.println(arraylist.toString());       
        } catch(Exception e) {
            System.out.println(e);
        }
    }
}

Answer 1

It's a bit odd requirement because you can only store Object in your class and you have to use instanceof when you get elements from a list. To convert the string a simple way is to try to convert and then catch but ignore any exception like this

public static Object convertToSomeNumber(String input) {
    try {
        return Integer.valueOf(input);
    } catch (Exception e) {
    }

    try {
        return Double.valueOf(input);
    } catch (Exception e) {
    }

    return null;
}

Now you can use it on your temp variable and add the result to the list if it is not null.

Note that I ignored Float so you need to add that yourself if you want to support it.