A java file containing two comparable programs using a list and a map.

listMap.java

import java.util.*;

record Data(String type, float amount, int quantity) {
}

record Datav2(float amount, int quantity) {
}

class ListyMain {

    public static void main(String[] args) {
        Random rand = new Random(0);
        var list = new ArrayList<Data>(Util.ELEMENT_COUNT);
        for (int i = 0; i < Util.ELEMENT_COUNT; i++) {
            list.add(Util.genData(rand));
        }

        // 302735752
        System.out.println(Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory());

        // print to avoid optimizing out the list.
        System.out.println(list);
    }
}

class MapyMain {

    public static void main(String[] args) {
        Random rand = new Random(0);
        var map = new HashMap<String, Datav2>();
        for (int i = 0; i < Util.ELEMENT_COUNT; i++) {
            map.compute(Util.genType(rand), (k, v) -> {
                if (v == null) {
                    v = new Datav2(0.0f, 0);
                }
                return new Datav2(v.amount() + Util.getAmount(rand), v.quantity() + Util.getQuantity(rand));
            });
        }

        // 18103344
        System.out.println(Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory());

        // print to avoid optimizing out the list.
        System.out.println(map);
    }
}

class Util {
    final static int ELEMENT_COUNT = 10_000_000;

    final static List<String> types = List.of("A", "B", "C");

    static Data genData(Random rand) {
        return new Data(genType(rand), getAmount(rand), getQuantity(rand));
    }

    static int getQuantity(Random rand) {
        return rand.nextInt(10);
    }

    static float getAmount(Random rand) {
        return rand.nextFloat() * (10);
    }

    static String genType(Random rand) {
        return types.get(rand.nextInt(types.size()));
    }
}