HashMap 1.2.0

HashMap is a data structure that implements a hash table, allowing for efficient storage and retrieval of key-value pairs.

HashMap handles collisions using techniques such as chaining (linking nodes in a list) or open addressing (finding the next available slot).

HashMap offers fast lookups, insertions, and deletions, with average time complexity of O(1). It's also dynamic, resizing as needed.

No, HashMap is not thread-safe. If multiple threads access it concurrently, external synchronization is necessary.

Yes, HashMap allows one null key and multiple null values.

The initial capacity of a HashMap is 16, with a load factor of 0.75 by default.

You can iterate over a HashMap using methods like entrySet(), keySet(), or values(). Each method returns a set or collection that you can loop through.

When the load factor threshold is breached, the HashMap automatically resizes (doubles its capacity) and rehashes the entries.

Yes, you can use custom objects as keys in a HashMap as long as you properly override the hashCode() and equals() methods.

The main differences include that Hashtable is synchronized (thread-safe) while HashMap is not, and that HashMap allows null keys and values while Hashtable does not.