Java ArrayList looking for multiple strings

Question

Let's say I have two same strings inside an ArrayList... is there a way to check for that? Also is there a way to check for how many times a string of the same exact is in the ArrayList?

So let's say I have the following a ArrayString.

os.println(itemIDdropped + "|" + spawnX + "|" + spawnY + "|" + currentMap + "|drop|" + me.getUsername());
1. 1|3|5|1|drop|Dan
2. 2|5|7|2|drop|Luke
3. 1|3|5|2|drop|Dan
4. 3|3|5|1|drop|Sally

Here is what the numbers/letters mean for the 1-4 strings... item ID, X pos, Y pos, Map it's on, command drop, user who dropped it

Then let's say I split it up doing this:

String[] itemGrnd = serverItems.get(i).split("\\|");

Now, let's say I have a for-loop like this one:

for (int i = 0; x < serverItems.size(); i++) {
    System.out.println(serverItems.get(i));
}

I want to find where X, Y, and Map or in this case itemGrnd[1], itemGrnd[2], and itemGrnd[3] are the same in ANY other String in the ArrayList I found via serverItems.get(i).

And if WE DO find any... (which in the example I provide above... x, y, and map are the same for 1 and 4... then create an IF statment to do it ONCE... because I don't want to do this: (BTW I do keep track of my variables for client-side so don't worry about that. Yes I know it's named spawnX and spawnY.. that's just the current X,Y.

if (spawnX.equals(Integer.parseInt(itemGrnd[1])) && 
    spawnY.equals(Integer.parseInt(itemGrnd[2])) &&
    currentMap.equals(Integer.parseInt(itemGrnd[3]))) {
}

Now, if I were to do THIS.... 1 and 4 were be processed through here. I Only want do it ONCE.. at ALL times if we find multple strings (like 1 and 4)

Thanks

Answer 1

Well, it's pretty simple to find out how many String ArrayList has:

public class ArrayListExample {
    private static final String TO_FIND = "cdt";

    public static void main(String[] args) {
        ArrayList<String> al = new ArrayList<String>();
        al.add("abc");
        al.add("dde");
        //4 times
        al.add(TO_FIND);
        al.add(TO_FIND);
        al.add(TO_FIND);
        al.add(TO_FIND);

        ArrayList<String> al1 = (ArrayList<String>) al.clone();
        int count = 0;
        while (al1.contains(TO_FIND)) {
            al1.remove(TO_FIND);
            count++;
        }
        System.out.println(count);
    }
}

Answer 2

A faster way would be to sort the ArrayList and then see how many different elements are there. Denis_k solution is the O(n^2) and with sorting it is O(nlog(n)).

Answer 3

If you want that kind of behavior, you might want to check the Apache Commons / Collections project, which extends the default java collections by some useful interfaces, including the bag interface (JavaDoc), which seems to be what you are looking for: a collection that knows how many elements of one kind it contains. The downside: there is no support for generics yet, so you are working with raw collections.

Or Google Guava, which is a more modern library and has a similar concept, called MultiSet which is probably more user-friendly. Guava however does not yet have a release version although it is already widely used in production.

Oh, and there's also a standard JavaSE function: Collections.frequency(Collection, Object), although it supposedly performs badly.