Collections.synchronizedMap(new HashMap());

Collections.synchronizedList(List<T> list)

In Java, if you want to make a Map or List thread-safe or synchronized, you can use the Collections.synchronizedMap and Collections.synchronizedList methods, respectively. These methods return synchronized versions of the provided Map or List. Here’s how you can use them:

For a Map:

java

Map<String, Object> synchronizedMap = Collections.synchronizedMap(new HashMap<>());

For a List:

java

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

By using these methods, you get a synchronized wrapper around the original Map or List. This means that each method of the synchronized Map or List is synchronized, providing thread safety. However, keep in mind that while these methods help with basic thread safety, you might still need additional synchronization for compound operations.

Alternatively, starting from Java 8, you can use the java.util.concurrent package which provides more sophisticated concurrent collections. For example, ConcurrentHashMap for a thread-safe Map or CopyOnWriteArrayList for a thread-safe List.

java

// For a thread-safe Map

Map<String, Object> concurrentMap = new ConcurrentHashMap<>();

// For a thread-safe List List<String> concurrentList = new CopyOnWriteArrayList<>();

These classes typically provide better performance in concurrent scenarios compared to the synchronized collections. Always choose the appropriate collection based on your specific use case and requirements.