How to Implement a Thread-Safe Resizable Array in Java?

Multiple threads may securely execute operations like insertion and deletion without risking data corruption when utilizing a thread-safe resizable array. The ArrayList class is a popular Java class, yet it is not thread-safe by default. We may use concurrent collections or synchronization to make it thread-safe.

Thread-Safe Resizable Array in Java

We may use concurrent collections like CopyOnWriteArrayList or Collections.synchronizedList to create a thread-safe resizable array. Data corruption is avoided via synchronization, which guarantees that only one thread may access the array at a time.

Program to Implement Thread Safe Resizable Array in Java

Using Collections.synchronizedList, let’s examine an example:

Java

// Java Program to Implement Thread Safe Resizable Array
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

// Driver Class
public class ThreadSafeResizableArray {
    // Main Function
    public static void main(String[] args) {
        // Creating a thread-safe resizable array
        List<Integer> threadSafeArray = Collections.synchronizedList(new ArrayList<>());

        // Adding elements in a thread-safe manner
        threadSafeArray.add(1);
        threadSafeArray.add(2);
        threadSafeArray.add(3);

        // Iterating over the array using a synchronized block
        synchronized (threadSafeArray) {
            for (Integer element : threadSafeArray) {
                System.out.println(element);
            }
        }
    }
}

Output

1
2
3

Explaination of the above Program:

In this example, we use Collections.synchronizedList to generate a thread-safe resizable array. An existing list is wrapped by the synchronizedList method, which then produces a synchronized (thread-safe) list.

As an alternative, CopyOnWriteArrayList may be utilized:

Java

// Java Program to Implement Thread Safe Resizable Array
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

public class ThreadSafeResizableArray {

    public static void main(String[] args) {
        // Creating a thread-safe resizable array
        List<Integer> threadSafeArray = new CopyOnWriteArrayList<>();

        // Adding elements
        threadSafeArray.add(1);
        threadSafeArray.add(2);
        threadSafeArray.add(3);

        // Iterating over the array
        for (Integer element : threadSafeArray) {
            System.out.println(element);
        }
    }
}

Output

1
2
3

Explaination of the above Program:

Concurrent collections like CopyOnWriteArrayList provide thread safety without requiring explicit synchronization. To ensure safe iteration, it makes a fresh duplicate of the underlying array each time an element is added or changed.