Java Coding Problems

Thread-safe map

The thread-safe version of a Map is ConcurrentHashMap.

The following table enumerates the Java built-in single-thread and multithreaded maps:

Single thread	Multithreaded
HashMap TreeMap (sorted keys) LinkedHashMap (maintain insertion order) IdentityHashMap (keys compared via ==) WeakHashMap EnumMap	ConcurrentHashMap ConcurrentSkipListMap (sorted map) Hashtable

ConcurrentHashMap allows retrieval operations (for example, get()) without blocking. This means that retrieval operations may overlap with update operations (including put() and remove()).

Creating a ConcurrentHashMap can be done as follows:

ConcurrentMap<Integer, Integer> map = new ConcurrentHashMap<>();

Whenever thread safety and high performance are ...