Implementing a factory design pattern for GA selection

Question

I've been working on different genetic algorithm selection methods recently. At the moment I have a RawFitnessSelction class, a RouletteWheelSelection class and a TournamentSelection class. I've been asked to use a factory/abstract factory pattern to choose the different selection methods. I think I'm going to go with a factory pattern as I don't fully understand abstract factory patterns but I'm wondering how to apply the actual pattern to something like GA selection methods?

public static Map<String, Double> rouletteSelect (Map<String, Double> population) {
    //Create a List (ArrayList) called rouletteSelect of type
    //Map<String, Double> and input values from our input Map.
    List<Map.Entry<String,Double>> sorted = new ArrayList<>(population.entrySet());

    //Use collections.sort to sort our "sorted" base on their values
    Collections.sort(sorted, Comparator.comparing(Map.Entry::getValue));

    //Initialize a HashSet
    Set<Integer> usedIndices = new HashSet<>();

    //Initialize our result Map<>, to store our selected individuals
    Map<String, Double> result = new HashMap<>();

    //we want to "select" half the individuals so while the size of our result 
    //is less than half, keep going
    while (result.size() < sorted.size()/2) {
        //pick a random int between 0 and the number of elements we have
        int index = rnd.nextInt(sorted.size());

        //if the element isn't in our set (a set can only contain one
        //occurrence of value x) do what is after our if, else it increments 
        //our while loop (it's already in our set)
        if(!usedIndices.add(index)) {
            continue;
        }
        //create a new Map, which has the <key,vale> of corresponding
        //index of "index" in sorted ArrayList
        Map.Entry<String, Double> survivor =sorted.get(index);
        //pur key and value from survivor into our result HashMap.
        result.put(survivor.getKey(), survivor.getValue());
    }
    return result;
}

Here's the basic structure of my selection methods. Just a basic method stored inside a class. Any help on how to implement the factory pattern to these types of methods would be appreciated.

Note: I know what my actual factory.java file will look like it's more so the abstact Selection.java class and the subclass RouletteWheel.java. Thanks

Answer 1

Map<String, Selection> selectionMap = new HashMap<>();
selectionMap.put("RawFitnessSelction", new RawFitnessSelction());
selectionMap.put("RouletteWheelSelection", new RouletteWheelSelection());
selectionMap.put("TournamentSelection", new TournamentSelection());

AbstractSelectionFactory asf = new DOSInputSelectionFactory(
    selectionMap, 
    "Input choice of selection method: ");

class Client {
    AbstractSelectionFactory asf;
    Client (AbstractSelectionFactory asf) { 
        this.asf = asf;
    }

    public void select(Map<String, Double> population) {
        Selection selection = asf.chooseSelection();
        ...
    }

An abstract factory can be passed to a client and called as many times as you like, or just once. So long as the Client never sees the abstract factory being built, it doesn't care if you're getting input from the command line, a GUI, a file, a database, the internet, or whatever else.