How does HashMap in Java deal with hash collisions?
In Java, HashMap resolves hash conflicts by using the method of chaining. When a hash conflict occurs, chaining will store conflicting key-value pairs in the same bucket using either a linked list or a red-black tree.
The specific steps for resolving hash conflicts are as follows:
- When inserting a key-value pair, first calculate the hash value of the key.
- Find the corresponding bucket based on the hash value.
- If the bucket is empty, simply insert the key-value pair into the bucket.
- If the bucket is not empty, then iterate through the linked list or red-black tree in the bucket.
- If the key already exists in the linked list or red-black tree, then update the corresponding value.
- If the key does not exist in the linked list or red-black tree, the key-value pair will be inserted at the end of the linked list or red-black tree.
- If the length of the linked list exceeds a certain threshold (default is 8), the linked list will be converted into a red-black tree.
- If the number of nodes in the red-black tree is less than or equal to 6, then convert the red-black tree into a linked list.
By using chaining method, HashMap can efficiently resolve hash collisions, with a time complexity of O(1) for most cases of insertion, retrieval, and deletion operations.