After JDK1.8, HashMap underlying data structure is an array of red and black + + book list.
We know from the source:
the list Hashmap in size when more than eight will be automatically converted into red-black tree, when deleting less than six changes to the list again, never asked why, Baidu wave.
The Poisson distribution, the default load factor of 0.75 when the number of elements in a single vessel hash probability is less than 8 parts per million, so that as a watershed to 7, the conversion is not equal to 7, when greater than or equal to 8 when it is time to convert, into less than or equal to 6 on the list.
Note: when 7 is not converted to the list.
