How to Make an ArrayList Thread-Safe When Storing Custom Thread Objects in Java?

Making ArrayList Thread-Safe in Java: An Alternative Approach

In the context of multithreaded programming, it is essential to ensure that shared resources, such as ArrayLists, are accessed safely to avoid data inconsistencies and concurrency issues. This article discusses an alternative approach to addressing the thread-safety of an ArrayList in Java, particularly when it contains custom objects that extend the Thread class.

In your specific scenario, you have an ArrayList that stores RaceCar objects, and a callback method (addFinisher) within a Race class that populates the ArrayList with completed RaceCar objects. However, you encountered an error when attempting to use the Collections.synchronizedCollection() method to make the ArrayList thread-safe.

The error you encountered stemmed from the type mismatch between Collection and ArrayList. Collections.synchronizedCollection() returns a Collection, whereas you were attempting to assign it to an ArrayList variable. Instead, you should utilize the Collections.synchronizedList() method, which returns a thread-safe ArrayList.

<code class="java">finishingOrder = Collections.synchronizedList(new ArrayList(numberOfRaceCars));</code>

By using Collections.synchronizedList(), you create a new synchronized ArrayList that wraps the underlying ArrayList. This synchronized list ensures that all access to the list is synchronized, preventing multiple threads from attempting to modify it concurrently.

This approach provides a convenient and effective way to make your ArrayList thread-safe while maintaining the functionality of your code. It allows you to safely add and retrieve RaceCar objects in a multithreaded environment without worrying about data integrity issues.

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