How to use Java Arrays -- Translating From Ruby to Java

Question

I'm just starting with Java, so I'm transcribing some of my Ruby stuff. I have a Ruby function like this, which generates something that looks like an IPv6 address:

def generate_ip()
    list = ["a", "b", "c", "d", "e", "f", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0"]
    address = ""
    8.times do
        4.times do
            address << list.shuffle[5]
        end
        address << ":"
    end
    return address[0..-2].to_sym
end

This method simply takes an array of strings and then repeatedly jumbles them up, choosing the 5th element each time to construct the returned string.

As far as I can tell, there's no "shuffle()" method for String Arrays in Java, so I figured I'd write my own. But then I started to get completely mired in sub-problems, such as:

1. Apparently there's no built-in way to remove items from a String Array, which seems strange -- is that correct? I saw several other SO posts where the responses for this features were a 10-line block of code. So I decided to use ArrayLists, since according to the doc, they have sane methods like size(), get(), and remove(), although...

2. ...I haven't found a way to instantiate them using a literal, or to add multiple items with a single method call. Every tutorial I see (including the official Oracle Java Tutorial) uses multiple calls to ArrayList.add(). That can't be the way to do it, can it?

3. etc.

So before I go spiraling down into sub-problem land and asking 50 different questions, I thought I'd ask how to solve the most important problem. Is there a simple way to translate the above Ruby code into Java?

FWIW, my in-progress "shuffle" method is below. I'm just looping array.length times, copying/removing a random element from the old array to a new array each time.

public ArrayList<String> shuffle(ArrayList<String> array) {
        Random generator = new Random();
        ArrayList<String> shuffled = new ArrayList<String>();

        for (int i = 0; i > array.size(); i++) {
            int index = generator.nextInt(array.size());

            String popped = array.get(index);
            array.remove(index);

            shuffled.add(popped);
        }


        return shuffled;
    }

Answer 1

If you create a List (either ArrayList or LinkedList), you can use Collections.shuffle()

ArrayList and LinkedList are both implementations of the List interface. I suspect either would be ok for your needs here, although the ArrayList would be preferable (being backed by an array). Here's the Java List tutorial.

Arrays are of a fixed length in Java, whereas a List is variable in size, and so the List is more appropriate in general for your above conversion. To create a list with a given set of starting elements, see Arrays.asList() e.g.

List stooges = Arrays.asList("Larry", "Moe", "Curly");

Answer 2

Collections.shuffle(List<?> list, Random rnd) built-in library available in java.

Randomly permute the specified list using the specified source of randomness. All permutations occur with equal likelihood assuming that the source of randomness is fair.

open jdk code.