如何使用Collection.sort（）对FastUtil BigList进行排序

Question

If i have arraylist i can use Collection.sort() what's very effective and fast. But now i have to use BigList to hold much elements of my object type, and i have to sort them by value, From object called JasPlayer kills as int and nickname as String.

I've tried to use Collection.sort() whats the best method to do that but i can't use it like normal List.

private BigList<JasPlayer> playerRankingPlaces;

public BigList<JasPlayer> getRanking() {
    return this.playerRankingPlaces;
}

public void addRankingElement(JasPlayer element) {
    this.playerRankingPlaces.add(element);
}

public void setRanking(BigList<JasPlayer> playerRanking) {
    this.playerRankingPlaces = playerRanking;
}

public void sortRankingList() {
    for(JasPlayer player : JasPlayerUtils.getPlayers()) {
        addRankingElement(player);
        long startTime = System.nanoTime();

           //THERE's Problem, i can't use biglist like normal list :\
        Collections.sort(playerRankingPlaces, Comparator.comparing(Ranking :: getKills).thenComparing(Ranking :: getName));


        long endTime = System.nanoTime() - startTime;
        MessageUtils.sendDebug("Sorting " + playerRankingPlaces.size() + "took " +  endTime / 1e9 + " seconds");
    }
}

private static int getKills(UUID uuid) {
    if(JasPlayerUtils.findByUUID(uuid).isPresent()) {
        return JasPlayerUtils.findByUUID(uuid).get().getKills();
    }
    return 0;
}

private static String getName(UUID uuid) {
    if(JasPlayerUtils.findByUUID(uuid).isPresent()) {
        return JasPlayerUtils.findByUUID(uuid).get().getPlayer().getName();
    }
    return "Brak";
}

Answer 1

I'm pretty sure you are suffering from the XY Problem . Fastutil's BigList is harder to use than normal lists and there is no reason to use it if the number of elements can't exceed Integer.MAX_VALUE.

If you really need it (say you really have 3000 millions of elements and need to store them in memory as a list) the way I found to sort a BigList is using the static sorting methods at the BigArrays class, mergesort and quicksort . They take as arguments:

• Starting (inclusive) and ending (exclusive) indexes to sort, ie 0 and the size of the list
• a LongComparator , which is an object that given two long indexes compares the elements at these indexes
• a BigSwapper, which is an object that given two long indexes swaps the elements at these indexes.

Example:

import it.unimi.dsi.fastutil.BigArrays;
import it.unimi.dsi.fastutil.BigList;
import it.unimi.dsi.fastutil.BigSwapper;
import it.unimi.dsi.fastutil.longs.LongComparator;
import it.unimi.dsi.fastutil.objects.ObjectBigArrayBigList;

public class App 
{
    public static void main( String[] args )
    {
        BigList<String> bigList = new ObjectBigArrayBigList<String>();
        bigList.add("Z");
        bigList.add("X");
        bigList.add("Y");
        bigList.add("A");
        bigList.add("C");
        bigList.add("B");

        System.out.println("Biglist before: " + bigList.toString());

        LongComparator cmp = (i,j) -> bigList.get(i).compareTo(bigList.get(j));
        BigSwapper swapper = (i,j) -> {
            String tmp = bigList.get(i);
            bigList.set(i, bigList.get(j));
            bigList.set(j, tmp);
        };

        BigArrays.mergeSort(0, bigList.size64(), cmp, swapper);

        System.out.println("Biglist after : " + bigList.toString());
     }
}

Output:

Biglist before: [Z, X, Y, A, C, B]
Biglist after : [A, B, C, X, Y, Z]