How is the Hashtable used in Java?

In Java, Hashtable is a class that implements the Map interface, capable of storing key-value pairs and retrieving values based on keys. The keys and values in Hashtable are objects, where keys cannot be duplicated but values can be.

The usage of Hashtable includes:

1. Add key-value pairs: Use the put() method to add key-value pairs to the Hashtable.
2. Get value: Retrieve the corresponding value using the get() method based on the key.
3. Check if a key is present: Use the containsKey() method to determine if a specific key is contained in the Hashtable.
4. Determine whether a value is included: Use the containsValue() method to check if a specific value is included in the Hashtable.
5. Remove key-value pair: Use the remove() method to delete the specified key-value pair based on the key.
6. Get the set of keys: Use the keySet() method to obtain a collection of all keys in the Hashtable.
7. Get the collection of values: use the values() method to obtain the collection of all values in the Hashtable.
8. Determine if the Hashtable is empty: Use the isEmpty() method to check if the Hashtable is empty.
9. To get the size of a Hashtable: use the size() method to determine the number of key-value pairs in the Hashtable.

Hashtable is a thread-safe class that can be used in a multi-threaded environment. It is important to note that Hashtable is a legacy class and is generally not recommended for use; instead, it is recommended to use the HashMap class as a replacement. Although the usage of HashMap and Hashtable is similar, HashMap has better performance.