Arrays of different types

Question

Is it possible to have an array that contains two different types of data? I want to have an array that contains a double and also a string. I attempted:

ArrayList<double><String> array;

But that didn't work.

Sorry for the silly question, but it has been a while since I have used something like this.. Can you refresh my memory on how would I declare and populate such an array?

And then to take it a step further, I would like to sort the array by the double if possible?

Thanks!

Answer 1

Firstly, it's worth being clear about the difference between an array and an ArrayList - they're not the same thing at all.

However, in either case you can't do what you want. The closest you can probably come is declaring your own type. (EDIT: My original code had a double or a string... I've now changed it to be a double and a string. Let me know if this change isn't what you had in mind.)

public final class DoubleAndString
{
    private final String stringValue;
    private final double doubleValue;

    public DoubleAndString(String stringValue, double doubleValue)
    {
        this.stringValue = stringValue;
        this.doubleValue = doubleValue;
    }

    public String getString()
    {
        return stringValue;
    }

    public String getDouble()
    {
        return doubleValue;
    }
}

Then create an ArrayList<DoubleAndString> or a DoubleAndString[].

Now, this feels somewhat vanilla at the moment - presumably the double and string values actually have a greater meaning - a name and a score, for example. If so, encapsulate that in a type which describes the pairing more appropriately.

As for ordering - you could make DoubleAndString implement Comparable<DoubleAndString> - but unless that's the only natural ordering which makes sense, I'd write a Comparator<DoubleAndString>:

public class DoubleComparator implements Comparator<DoubleAndString>
{
    public int compare(DoubleAndString ds1, DoubleAndString ds2)
    {
        return Double.compare(ds1.getDouble(), ds2.getDouble());
    }
}

Then you can use Collections.sort to sort an ArrayList<DoubleAndString> or Arrays.sort to sort an array.

Answer 2

You can use ArrayList<Object> and you can then use anything you'd like. Encapsulate the double in a Double object and when you retrieve the object use instanceof to check if it's really a double or a String.

I must say, it's unlikely this 'design' would win you any awards. Is it possible to rethink the solution you're considering for your problem, and see if you could do with a different kind of approach?