A HashMap is a part of the Java Collections Framework and is used to store data in key-value pairs. It allows one null key and multiple null values, and it is not synchronized, making it faster but not thread-safe. A Hashtable is a legacy class in Java that also stores data in key-value pairs. It does not allow null keys or values and is synchronized, making it thread-safe but slower compared to HashMap.
| Feature | HashMap | Hashtable |
|---|---|---|
| Null Values/Keys | Allows one null key and multiple null values | Does not allow null keys or values |
| Synchronized | Not synchronized, not thread-safe | Synchronized, thread-safe |
| Performance | Faster, as it is not synchronized | Slower, due to synchronization overhead |
| Iteration Order | Does not guarantee any order | Does not guarantee any order |
| Package | java.util | java.util |