On Sat, 9 Apr 2022 16:02:17 GMT, liach <d...@openjdk.java.net> wrote:
> > > Quick question: If the maps are intended to be fixed-size, can't the > > > users just call `new HashMap<>(size, 1)`, increasing the growth factor to > > > prevent growth? > > > > > > @liach this questions equals question : "why default load factor be 0.75 > > not 1" In short, when larger the load factor, smaller memory use, and > > larger hash-collide rate, larger crud time cost. when smaller the load > > factor, larger memory use, and smaller hash-collide rate, smaller crud time > > cost. As for why default load factor be 0.75 but not 1, it is historical to > > me. it is already 0.75 when I first learn java and never changed then. But > > I guess there be some empirical formula behind it. > > No. I mean when the growth factor is 1 and exactly `size` key-value pairs are > put into the map, the map will not grow; but when it's 0.75, the map will > preemptively grow erroneously. Changing the growth factor is effectively > no-op for a hash map that will not have more elements added later during its > usage. I don't think you get what I mean. For example. There be a people who want a 16-elements map. If use `new HashMap(16 , 1)`, then he will get a table-length-16 hashMap. It will not growth, wth larger load factor, smaller memory use, and larger hash-collide rate, larger crud time cost. if use `new HashMap(22, 0.75)`, （` 22 = Math.celil(16 / 0.75)`）then he will get a table-length-32 hashMap. It will not growth, with smaller load factor, larger memory use, and smaller hash-collide rate, smaller crud time cost. I hope the example can help you understand what is load factor's usage, and be clear about the difference between using 0.75 and 1 as load factor. ------------- PR: https://git.openjdk.java.net/jdk/pull/7928
