How is the organization of elements with the same hash code inside HashMap implemented?

In Java, HashMap elements with the same hash code (collisions) are organized as a linked list or, starting from Java 8, when there are many collisions — as a balanced tree (TreeNode).

When multiple keys have the same hash code, they are placed in one "bucket." Initially, all elements in a bucket are linked through a singly linked list. If the number of elements in a bucket exceeds a certain threshold (usually 8), the list is transformed into a red-black tree to improve search efficiency.

An example of a simplified structure:

static class Node<K,V> implements Map.Entry<K,V> {
    final int hash;
    final K key;
    V value;
    Node<K,V> next;
    // ...
}

Thus, in case of collisions, HashMap first searches for an element in the list or tree by key, comparing keys using equals().