Synchronized Java Collections: Collections.synchronizedList and synchronized

When working with Java Collections in multi-threaded environments, it's important to ensure that the collections are thread-safe. Synchronization is the process of ensuring that only one thread can access a resource at a time. In Java, there are two ways to synchronize collections: using the Collections.synchronizedList() method and using the synchronized keyword.

Collections.synchronizedList()

The Collections.synchronizedList() method returns a synchronized (thread-safe) list backed by the specified list. Any method that modifies the returned list is synchronized on the returned list itself. In other words, the entire list is locked during modification, preventing other threads from accessing the list at the same time. Here's an example:

List<String> myList = new ArrayList<>();
List<String> synchronizedList = Collections.synchronizedList(myList);

Now, any modification to the synchronizedList will be synchronized:

synchronizedList.add("Item 1");

synchronized Keyword

The synchronized keyword is used to define a synchronized block of code. Any code placed inside a synchronized block is locked, preventing other threads from accessing the same code at the same time. Here's an example:

List<String> myList = new ArrayList<>();

synchronized(myList) {
    myList.add("Item 1");
}

Here, the myList is locked during the add() method call, preventing other threads from accessing the same list at the same time.

Conclusion

Both Collections.synchronizedList() and the synchronized keyword can be used to synchronize Java collections in multi-threaded environments. However, it's important to note that Collections.synchronizedList() provides better performance and is easier to use, especially when dealing with complex data structures. On the other hand, the synchronized keyword provides more fine-grained control over synchronization, allowing for greater flexibility.