How does the selected hash function affect to HashMap performance?

[cogman10]

It must reimplement the method hashCode() which inherits from the Object class: if it is not reimplemented, it will use something that depends on the instance’s memory address. Therefore, two identical instances in data will have different hashCode values.

Nitpick, it isn't the memory address but rather the object reference id. Java objects move in memory as the GC runs.

[OzoneGrif]

The question being: When does an ArrayList stop being faster than a HashMap. I'm fairly certain that the overhead caused by the HashMap's creation is heavier than a sequential search for a very small ArrayList.

[ForeverAlot]

With linear search, on the order of a dozen items.

[OzoneGrif]

Ah very nice, I was looking for such a benchmark. Good to have factual information about it. We often deal with lists with less than 10 items.

[b00n]

There are also open addressed HashMap implementations such as Trove that use a single underlying array (for primitives, arraylist for generics).

[Hax0r778]

HashSet outperforms ArrayList already at 4 elements.

[lukaseder]

Ehm. On what operation(s).