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Why HashMap's loading factor is 0.75, I believe many inexperienced people are helpless about this, this article summarizes the causes and solutions of the problem, through this article I hope you can solve this problem.

Why does HashMap need to load factors?

The bottom layer of HashMap is hash table, which is the structure type of storing key-value pairs. It needs certain calculations to determine the storage location of data in hash table:

static final int hash(Object key) { int h; return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);}// AbstractMappublic int hashCode() { int h = 0; Iterator i = entrySet().iterator(); while (i.hasNext()) h += i.next().hashCode(); return h;}

General data structure, either query fast or insert fast, HashMap is a slow insert, query fast data structure.

However, this data structure is prone to two problems: ① if the space utilization rate is high, then when the hash algorithm calculates the storage location, it will find that many storage locations already have data (hash conflict);② If in order to avoid hash conflict, increase the array capacity, it will lead to low space utilization.

The load factor is the degree to which the elements in the Hash table are filled.

Load Factor = Number of elements filled in table/Length of hash table

The larger the loading factor, the more elements are filled, the higher the space utilization rate, but the chance of conflict becomes larger.

The smaller the load factor, the less elements are filled, the less chance of collisions, but the more space is wasted, and the higher the number of expansion rehashes.

The greater the chance of conflict, the more expensive it is to find data that needs to be found in another way. Therefore, a balance and compromise must be found between "opportunities for conflict" and "space utilization."

What are the ways to resolve conflicts? 1. Open addressing Hi = (H(key) + di) MOD m, where i=1,2,…,k(k

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