/**
 * SkimpyMap is map with minimal footprint
 *
 * - contains no buckets
 * - contains from 0 to 2 keys
 * - lookup is linear :)
 * - lookup is still fast because of ... Aha-ha..:)
 */
public class SkimpyMap<K,V> implements Map<K,V> {

    public static final int MAX_KEYS = 2;

    private Object[] keys;
    private Object[] values;

    .....

@State(Scope.Thread)
@BenchmarkMode(Mode.Throughput)
@Warmup(iterations = 1)
@Fork(1)
@Measurement(iterations = 3)
public class MyBenchmark {

    private SkimpyMap<String,String> skimpyMap = new SkimpyMap<>();

    private Map<String, String> hashMap = new HashMap<>();

    private Map<String, String> javaTreeMap = new HashMap<>();

    @Setup
    public void setup() {

    }

    @Benchmark
    public void skimpy() {
        skimpyMap.put("1","");

        skimpyMap.put("2","");
        skimpyMap.remove("1");

        skimpyMap.put("3","");
        skimpyMap.remove("2");

        skimpyMap.put("4","");
        skimpyMap.remove("3");

        skimpyMap.remove("4");

        skimpyMap.clear();
    }

    @Benchmark
    public void hash() {
        hashMap.put("1","");

        hashMap.put("2","");
        hashMap.remove("1");

        hashMap.put("3","");
        hashMap.remove("2");

        hashMap.put("4","");
        hashMap.remove("3");

        hashMap.remove("4");

        hashMap.clear();
    }

    @Benchmark
    public void tree() {
        javaTreeMap.put("1","");

        javaTreeMap.put("2","");
        javaTreeMap.remove("1");

        javaTreeMap.put("3","");
        javaTreeMap.remove("2");

        javaTreeMap.put("4","");
        javaTreeMap.remove("3");

        javaTreeMap.remove("4");

        javaTreeMap.clear();
    }

Benchmark            Mode  Cnt         Score         Error  Units
MyBenchmark.hash    thrpt    3  16026559.188 ± 2335586.914  ops/s
MyBenchmark.skimpy  thrpt    3  15609958.668 ± 3353609.697  ops/s
MyBenchmark.tree    thrpt    3  15744633.323 ± 1522374.688  ops/s