convert ArrayList.toString() back to ArrayList in one call

Question

I have a toString() representation of an ArrayList.

Copying the toString() value to clipboard, I want to copy it back into my IDE editor, and create the ArrayList instance in one line. In fact, what I'm really doing is this:

• my ArrayList.toString() has data I need to setup a unit test.
• I want to copy this ArrayList.toString() into my editor to build a test against this edge case
• I don't want to parse anything by hand

My input looks like this:

[15.82, 15.870000000000001, 15.92, 16.32, 16.32, 16.32, 16.32, 17.05, 17.05, 17.05, 17.05, 18.29, 18.29, 19.16]

The following do not work:

• Arrays.asList()
• google collections Lists.newArrayList()

Suggestions?

Answer 1

Substring the braces away, split it on , (comma and space) and finally feed it to Arrays#asList().

 String s = "[15.82, 15.870000000000001, 15.92, 16.32, 16.32, 16.32, 16.32, 17.05, 17.05, 17.05, 17.05, 18.29, 18.29, 19.16]";
 List<String> list = Arrays.asList(s.substring(1, s.length() - 1).split(", "));

Note that this will work in your particular case, but not in all circumstances. You may for example have a list of strings of which at least one contains a subsequent comma and space. The split would then fail.

Answer 2

Generally speaking the toString() of any objects does not contain information to reproduce the original object without any further information.

In your specific case the example could be produced by many different ArrayList instances (as well as pretty much all other List implementations which have identical toString()) implementations.

As an extreme example, think of an ArrayList that contains a single element which is the String with the content 15.82, 15.870000000000001, 15.92, 16.32, 16.32, 16.32, 16.32, 17.05, 17.05, 17.05, 17.05, 18.29, 18.29, 19.16. That ArrayList would produce the exact same output as your original ArrayList. And since two different inputs produce the same output, there's no way this function can be reversed without additional information.

If, however, we have additional information, such as the content type of the original ArrayList, then it becomes possible in some cases. If we know that all elements of the List were of type Double, then it's actually pretty easy:

public static List<Double> stringToList(final String input) {
    String[] elements = input.substring(1, input.length() - 1).split(", ");
    List<Double> result = new ArrayList<Double>(elements.length);
    for (String item : elements) {
        result.add(Double.valueOf(item));
    }
    return result;
}

Granted, it's not a one-liner, but it's not too bad.