How does HashMap work?

The principle is introduced as follows:

HashMap is implemented based on the Hash algorithm.

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When using the put(key,value) method, HashMap will be obtained based on the key.hashCode() method Get the hash value of the key, and then find the corresponding bucket position based on the hash value. If there is already an element in this area, another euqal() comparison will be done. If they are equal, the new addition will fail because HashMap does not allow the same key value. , if not equal, it is just a simple hash conflict.

Before JDK1.8, HashMap will store this element in the next node of the linked list. HashMap stores key-value pairs in each linked list node. After JDK1.8, HashMap added a red-black tree, so when the number of linked list nodes exceeds 8, it will be converted from the linked list to a red-black tree, and once it is less than 8, it will be converted from the red-black tree back to the linked list.

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