Collections.synchronizedMap()

In Java, Collections.synchronizedMap() is used to create a thread-safe map. It wraps any existing map with synchronization to ensure safe concurrent access by multiple threads. This is particularly useful in scenarios where multiple threads may add, remove, or query elements from the map simultaneously.

The syntax for creating a synchronized map is similar to other synchronized collections in Java:

Map<K, V> synchronizedMap = Collections.synchronizedMap(new HashMap<K, V>());Code language: HTML, XML (xml)

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

public class SynchronizedMapExample {

    public static void main(String[] args) {
        // Create a normal HashMap to store student grades
        Map<String, Integer> studentGrades = new HashMap<>();
        
        // Adding student grades to the map
        studentGrades.put("Paani", 85);
        studentGrades.put("Mahesh", 78);
        studentGrades.put("Datta", 90);
        studentGrades.put("Ganesh", 92);
        studentGrades.put("Harsha", 88);
        
        // Create a synchronized map
        Map<String, Integer> synchronizedStudentGrades = Collections.synchronizedMap(studentGrades);
        
        // Adding a new student grade to the synchronized map
        synchronizedStudentGrades.put("New Student", 95);
        
        // Removing a student grade from the synchronized map
        synchronizedStudentGrades.remove("Harsha");
        
        // Displaying the contents of the synchronized map
        System.out.println("Synchronized student grades:");
        synchronized (synchronizedStudentGrades) {
            for (Map.Entry<String, Integer> entry : synchronizedStudentGrades.entrySet()) {
                System.out.println(entry.getKey() + " : " + entry.getValue());
            }
        }
    }
}

/*
D:\javaplanet\Collection Framework>javac SynchronizedMapExample.java

D:\javaplanet\Collection Framework>java SynchronizedMapExample
Synchronized student grades:
Ganesh : 92
Datta : 90
Mahesh : 78
Paani : 85
New Student : 95
*/

Benefits of Using Collections.synchronizedMap()

• Thread Safety: The synchronized map ensures that it can be safely accessed and modified by multiple threads concurrently, preventing issues like concurrent modification exceptions.
• Compatibility: It works seamlessly with existing code that relies on the Map interface, providing thread safety without needing manual synchronization.
• Ease of Use: It’s straightforward to convert an existing map into a synchronized map using Collections.synchronizedMap(), making it easy to integrate into Java applications.

Considerations

• Performance: While Collections.synchronizedMap() provides thread safety, it may not be the most performant solution for highly concurrent applications compared to other concurrent collections like ConcurrentHashMap. Evaluate performance requirements and usage patterns to choose the most appropriate collection type.
• Iterating and Atomicity: Although iterating over a synchronized map is safe, other compound operations (like iterating and then modifying the map) still require external synchronization to maintain atomicity.

Collections.synchronizedMap() in Java is a useful utility for ensuring thread-safe access to maps in multi-threaded applications. It simplifies the process of making collections thread-safe and helps in maintaining data consistency when accessed concurrently by multiple threads. Adjustments can be made based on specific application needs or integrated with other Java concurrency utilities for enhanced performance and scalability.