# What is the basic implementation principle of a hashmap?

The basic implementation principle of HashMap is based on the data structure of a hash table.HashMap maintains an array internally, where each element of the array is called a bucket, and each bucket stores a linked list (or a red-black tree) data structure. When storing key-value pairs, HashMap determines the storage position based on the hash value of the key, and then stores the key-value pair in the corresponding bucket.

When retrieving the value corresponding to a key, HashMap will locate the bucket based on the hash value of the key, and then search within the bucket to see if the key-value pair exists. Since different keys may have the same hash value, multiple key-value pairs may exist in the same bucket, and in these cases, the specific key-value pair is determined by comparing the keys using the equals method.

When performing put and get operations, HashMap uses the hash value of the key to determine the storage position, and then uses the equals method of the key to determine if the same key exists. If the same key exists, the corresponding value will be updated; if the same key does not exist, a new key-value pair will be added to the bucket.

HashMap internally uses a hash function to calculate the hash value of keys, and this function should minimize hash collisions, where different keys are mapped to the same bucket. In Java, the implementation of the hash function involves further processing of the hash value returned by the keys’ hashCode method to ensure an even distribution. HashMap also provides parameters to adjust the number of buckets and load factor to optimize the performance and space utilization of the hash table.