Mastering Hashtable in Java: Efficient, Thread-Safe, and Reliable Data Management

What is a Hashtable in Java?

• A Hashtable in Java is a collection that stores key-value pairs, similar to a map, where each key is related with a value.
• It is a part of the java.util package and was one of the initial classes given by Java.
• A Hashtable is comparable to the HashMap class, but it has a few imperative contrasts, especially in terms of synchronization and dealing with of null values.
• A Hashtable actualizes the Map interface and is used to store information in key-value pairs.
• The essential highlight of a Hashtable is its capacity to rapidly retrieve values based on the key, using a hashing algorithm to map the key to a particular bucket where the value is stored.

Key Highlights of Hashtable

1.Key-Value Pair Storage:

• In a Hashtable, information is stored as key-value pairs.
• Each key is special, and it maps to one value.
• In case a new key-value pair with an existing key is added, the old value is replaced.

2.Synchronization:

• A Hashtable is synchronized, meaning it is thread-safe and can be utilized safely by numerous threads at the same time.
• This makes it appropriate for multi-threaded applications, in spite of the fact that the synchronization makes it slower compared to HashMap (which isn’t synchronized).

3.Null Keys and Values:

• Not at all like HashMap, a Hashtable does not permit null keys or null values.
• Endeavoring to insert a null key or null value will result in a NullPointerException.

4.Proficient Lookups:

• The primary advantage of using a Hashtable is its capacity to perform productive lookups.
• It uses hashing to store and retrieve information, which guarantees that the average time complexity for lookup, insert, and delete operations is O(1), making it exceedingly proficient.

Types of Hash Tables

There are no explicit types of Hashtable in Java itself, but you’ll be able implement distinctive variations or behaviors depending on the application. In any case, in common, hash tables can be categorized based on the basic usage approach:

1.Open Addressing Hash Table (Linear Probing, Quadratic Probing):

• In this type of hashing, when a collision happens (i.e., two keys hash to the same index), an elective index is computed using a probing sequence.

2.Chaining Hash Table:

• This strategy uses linked lists (or other data structures like balanced trees) to handle collisions.
• Each bucket within the hash table contains a list of entries that hash to the same location.
• Java’s Hashtable uses this strategy for collision determination.

3.Thread-Safe Hash Table:

• As said prior, Hashtable is synchronized, which makes it thread-safe.
• In any case, this comes with overhead.
• To improve performance in multi-threaded situations, the ConcurrentHashMap (available in Java 5 and afterward) is suggested because it gives thread-safety without locking the entire table.

Example 1:Basic Hashtable Usage

Let’s see a basic example of how a Hashtable can be utilized to store and retrieve key-value pairs.

import java.util.*;

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

// Adding key-value pairs
hashtable.put("Apple", 10);
hashtable.put("Banana", 20);
hashtable.put("Cherry", 30);

// Displaying the Hashtable
System.out.println("Hashtable: " + hashtable);

// Retrieving a value using the key
System.out.println("Value for 'Apple': " + hashtable.get("Apple"));

// Removing a key-value pair
hashtable.remove("Banana");
System.out.println("After removing 'Banana': " + hashtable);

// Checking if a key exists
System.out.println("Contains 'Cherry'? " + hashtable.containsKey("Cherry"));

// Size of the Hashtable
System.out.println("Size of Hashtable: " + hashtable.size());
}
}

Output:

Hashtable: {Apple=10, Banana=20, Cherry=30}
Value for 'Apple': 10
After removing 'Banana': {Apple=10, Cherry=30}
Contains 'Cherry'? true
Size of Hashtable: 2

In this example:

1. We made a Hashtable and included three key-value pairs.
2. We retrieved the value related with the key “Apple”.
3. We removed the entry with the key “Banana”.
4. We checked in case the map contains a particular key (“Cherry”).
5. At last, we printed the size of the Hashtable.

Example 2:Hashtable with Thread Safety

Whereas Hashtable is synchronized, the execution can corrupt in a multi-threaded environment due to locking. Here’s an example of a basic thread-safe operation utilizing Hashtable.

import java.util.*;

public class ThreadSafeHashtable {
public static void main(String[] args) {
Hashtable<String, Integer> hashtable = new Hashtable<>();

// Adding key-value pairs in a thread-safe way
synchronized (hashtable) {
hashtable.put("Red", 1);
hashtable.put("Blue", 2);
hashtable.put("Green", 3);
}

// Reading data safely
synchronized (hashtable) {
System.out.println("Value for 'Red': " + hashtable.get("Red"));
}
}
}

Within the above example, we utilize synchronization blocks to guarantee that as it were one thread can access the Hashtable at a time. Be that as it may, in a modern multi-threaded application, using ConcurrentHashMap would be a higher choice because it gives more effective concurrency dealing with.