Hashtable and its features

A Hashtable in Java is a legacy data structure that implements the Map interface and provides a way to store key-value pairs. It is similar to HashMap but is synchronized, making it thread-safe for use in concurrent environments. Hashtable organizes its elements based on their hash codes and allows for fast retrieval, insertion, and deletion of elements.

Features of Hashtable:

• 1. Key-Value Pairing: Hashtable stores elements as key-value pairs, where each key is associated with exactly one value. Keys are used to retrieve their corresponding values.
• 2. Synchronized: Hashtable is synchronized, meaning that it is thread-safe for use in multi-threaded environments. This ensures that multiple threads can access and modify a Hashtable concurrently without causing data corruption or inconsistency.
• 3. Fast Lookup Operations: Hashtable provides fast lookup operations based on keys. You can retrieve the value associated with a key quickly using the get() method.
• 4. No Duplicate Keys: Each key in a Hashtable must be unique. If an attempt is made to add a duplicate key, the new value will overwrite the existing value associated with that key.
• 5. Null Keys and Values: Hashtable does not allow null keys or values. If a null key or value is attempted to be inserted into the Hashtable, it will throw a NullPointerException.
• 6. Hash-based Organization: Hashtable organizes its elements internally based on their hash codes, which allows for efficient storage and retrieval of elements.
• 7. Initial Capacity and Load Factor: Hashtable allows specifying an initial capacity and load factor at the time of creation. The initial capacity represents the initial size of the Hashtable, while the load factor determines when the Hashtable should resize itself to accommodate more elements.
• 8. Enumeration Support: Hashtable provides support for enumeration through its elements using the elements() and keys() methods.

```java
import java.util.Hashtable;
import java.util.Map;

public class HashtableExample {
    public static void main(String[] args) {
        // Create a Hashtable
        Map<String, Integer> hashtable = new Hashtable<>();

        // Add key-value pairs to the Hashtable
        hashtable.put("Apple", 10);
        hashtable.put("Banana", 20);
        hashtable.put("Cherry", 15);

        // Get the value associated with a key
        int value = hashtable.get("Banana");
        System.out.println("Value associated with 'Banana': " + value);

        // Remove a key-value pair from the Hashtable
        hashtable.remove("Cherry");

        // Print all key-value pairs in the Hashtable
        System.out.println("Key-Value Pairs:");
        for (Map.Entry<String, Integer> entry : hashtable.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}
```

In this example:

• We create a Hashtable and add some key-value pairs to it.
• We retrieve the value associated with the key “Banana” and remove the key-value pair associated with the key “Cherry” from the Hashtable.
• Finally, we iterate over all key-value pairs in the Hashtable and print them out.

Hashtable is commonly used in scenarios where thread safety is required or when working with legacy code that requires synchronization. However, in modern Java development, ConcurrentHashMap from the java.util.concurrent package is preferred over Hashtable for concurrent use cases due to better performance and scalability.