How does inserting an element into a HashMap data structure occur?

In Java, the HashMap data structure is implemented based on an array of buckets, each of which contains a linked list (or a tree if there are many elements). The insertion of an element occurs as follows:

1. The hash code of the key is computed using the hashCode() method.
2. The hash code is transformed into an array index (bucket) using a modulo operation or bit masking.
3. It checks whether an element with the same key already exists in the bucket (comparison via equals()).
4. If the key is found, the value is updated.
5. If the key is not found, a new entry is created and added to the beginning of the bucket's list (or to the tree).

Example:

HashMap<String, Integer> map = new HashMap<>();
map.put("key", 1);

Inside put, the index is calculated and the key-value pair is added to the corresponding bucket.

If the number of elements exceeds the load factor threshold, a rehash occurs with an increase in the array size.