How to Create a Synchronized HashTable in Java?

In Java, a synchronized HashTable is achieved by wrapping a regular HashTable with the Collection.synchronizedMap( ) method. This wrapper ensures that each method of the Map interface is synchronized, making the HashTable thread-safe.

Syntax:

Map<KeyType, ValueType> synchronizedHashTable = Collections.synchronizedMap(new HashTable<>());

Parameters:

• keyType: The type of keys in the HashTable.
• valueType: The type of values in the HashTable.

Approaches:

• Use the Collections.synchronizedMap( ) method to wrap a regular HashTable.
• Ensure that all read and write operations on the HashTable are performed using the synchronized wrapper.

Program to Create a Synchronized HashTable in Java

Below are the code implementations using the above two approaches.

Approach 1: Using Collections.synchronizedMap()

Below is the Program to create a synchronized HashTable using Collections.synchronizedMap().

Java

// Java program to Create a synchronized HashTable
// Using Collections.synchronizedMap( )
import java.io.*;
import java.util.*;

class SynchronizedHashTable {
    public static void main (String[] args) {
      // Create a hash table
      Map<String, Integer> hashTable = new HashMap();

      // Wrap the hash table with a synchronized map
      Map<String, Integer> synchronizedHashTable = Collections.synchronizedMap(hashTable);

      // Perform operations on the synchronized hash table
      synchronizedHashTable.put("one", 1);
      synchronizedHashTable.put("Two", 2);
      synchronizedHashTable.put("Three",3);

      // Iterate over the synchronized hash table
      synchronized (synchronizedHashTable) {
        for (Map.Entry<String, Integer> entry : synchronizedHashTable.entrySet()) {

        System.out.println("Synchronized HashTable is: " + entry.getKey() + ": " + entry.getValue());
       }
     }
  }
}

Output

Synchronized HashTable is: one: 1
Synchronized HashTable is: Two: 2
Synchronized HashTable is: Three: 3

Explanation of the above Program:

• We have created a HashMap named hashTable.
• We have used the Collections.synchronizedMap method to create a synchronized version of hashTable named synchronizedHashTable.
• Then we performed operations like put on the synchronizedHashTable.
• After that we iterate over the synchronizedHashTable using the enhanced for loop.
• At last, it prints the key-value pairs from the synchronized hash table.

Approach 2: Using Concurrent Class

Below is the Program to Create a Synchronized HashTable using Concurrent Class

Java

// Java program to create a synchronized HashTable
// Using concurrent class
import java.util.*;
import java.util.concurrent.*;

public class ConcurrentHashTable {
    public static void main(String[] args) {
        // Create a concurrent Hash Table
        ConcurrentHashMap<String, Integer> concurrentHashTable = new ConcurrentHashMap<>();

        // Perform operations on the concurrent Hash Table
        concurrentHashTable.put("one", 1);
        concurrentHashTable.put("two", 2);
        concurrentHashTable.put("three", 3);

        // Iterate over the concurrent hash table
        for (Map.Entry<String, Integer> entry : concurrentHashTable.entrySet()) {
            System.out.println("Synchronized HashTable is: " + entry.getKey() + ": " + entry.getValue());
        }
    }
}

Output

Synchronized HashTable is: one: 1
Synchronized HashTable is: two: 2
Synchronized HashTable is: three: 3

Explanation of the above Program:

• First, we have created a ConcurrentHashMap named concurrentHashTable.
• Then we perform operations like put() method on the concurrentHashTable.
• After that we iterate over the concurrentHashTable using the enhanced for loop.
• At last, it prints the key-value pairs from the concurrent hash table.