What are the differences between a HashMap and a Hashtable in Java?

There are several differences between a HashMap and a Hashtable in Java:

1. Synchronization: Hashtable is synchronized, while HashMap is not. This means that Hashtable is thread-safe, while HashMap is not. If you need a thread-safe map, you should use Hashtable or one of the other concurrent maps provided by the java.util.concurrent package.

2. Null keys and values: Hashtable does not allow null keys or values, while HashMap allows one null key and any number of null values.

3. Performance: Hashtable is generally slower than HashMap due to its synchronization. If you don't need the thread-safety provided by Hashtable, you should use HashMap for better performance.

4. Iteration order: Hashtable iterates over the elements in the order they were added, while HashMap does not make any guarantees about the iteration order. The order of the elements in a HashMap may change if the map is modified.

5. Methods: Hashtable has a number of legacy methods that are not present in HashMap, such as enumerate(), keys(), and elements(). These methods have been replaced by newer methods in HashMap, such as entrySet(), keySet(), and values().

6. Type parameters: Hashtable was introduced in Java 1.0, and does not use type parameters. To use a Hashtable with a specific key and value type, you need to use type casting. In contrast, HashMap was introduced