JAVA: Set lepszy do .contain niż ArrayList

Dzisiaj takie święto, więc przy okazji - a w zasadzie to bez okazji, ale święto jest ;) - napiszę o takiej ciekawostce jak z tytułu.

Zebrałem ciekawe wypowiedzi stąd:

The set will give much better performance (O(n) vs O(n^2) for the list), and that's normal because set membership (the contains operation) is the very purpose of a set.
Contains for a HashSet is O(1) compared to O(n) for a list, therefore you should never use a list if you often need to run contains.

I've made a test so please check the result:
For SAME STRING items in a HashSet, TreeSet, ArrayList and LinkedList, here are the results for 

1. 50.000 UUIDs

• SEARCHED ITEM : e608c7d5-c861-4603-9134-8c636a05a42b (index 25.000)

• hashSet.contains(item) ? TRUE 0 ms

• treeSet.contains(item) ? TRUE 0 ms

• arrayList.contains(item) ? TRUE 2 ms

• linkedList.contains(item) ? TRUE 3 ms 

2. 5.000.000 UUIDs

• SEARCHED ITEM : 61fb2592-3186-4256-a084-6c96f9322a86 (index 25.000)

• hashSet.contains(item) ? TRUE 0 ms

• treeSet.contains(item) ? TRUE 0 ms

• arrayList.contains(item) ? TRUE 1 ms

• linkedList.contains(item) ? TRUE 2 ms 

3. 5.000.000 UUIDs

• SEARCHED ITEM : db568900-c874-46ba-9b44-0e1916420120 (index 2.500.000)

• hashSet.contains(item) ? TRUE 0 ms

• treeSet.contains(item) ? TRUE 0 ms

• arrayList.contains(item) ? TRUE 33 ms

• linkedList.contains(item) ? TRUE 65 ms

Based on above results, there is NOT a BIG difference of using array list vs set. Perhaps you can try to modify this code and replace the String with your Object and see the differences then... 

A tu jest kodzik do testowania:

    public static void main(String[] args) {
        Set<String> hashSet = new HashSet<>();
        Set<String> treeSet = new TreeSet<>();
        List<String> arrayList = new ArrayList<>();
        List<String> linkedList = new LinkedList<>();

        List<String> base = new ArrayList<>();

        for(int i = 0; i<5000000; i++){
            if(i%100000==0) System.out.print(".");
            base.add(UUID.randomUUID().toString());
        }

        System.out.println("\nBase size : " + base.size());
        String item = base.get(25000);
        System.out.println("SEARCHED ITEM : " + item);

        hashSet.addAll(base);
        treeSet.addAll(base);
        arrayList.addAll(base);
        linkedList.addAll(base);

        long ms = System.currentTimeMillis();
        System.out.println("hashSet.contains(item) ? " + (hashSet.contains(item)? "TRUE " : "FALSE") + (System.currentTimeMillis()-ms) + " ms");
        System.out.println("treeSet.contains(item) ? " + (treeSet.contains(item)? "TRUE " : "FALSE") + (System.currentTimeMillis()-ms) + " ms");
        System.out.println("arrayList.contains(item) ? " + (arrayList.contains(item)? "TRUE " : "FALSE") + (System.currentTimeMillis()-ms) + " ms");
        System.out.println("linkedList.contains(item) ? " + (linkedList.contains(item)? "TRUE " : "FALSE") + (System.currentTimeMillis()-ms) + " ms");
    }

Bardzo mnie interesuje co o tym sądzisz, dlatego byłoby mi miło, jeśli byś napisał w komentarzu coś o tym, może być cokolwiek :)