Thejava.util.concurrent
package includes a number of additions to the Java Collections Framework. These are most easily categorized by the collection interfaces provided:
BlockingQueue
defines a first-in-first-out data structure that blocks or times out when you attempt to add to a full queue, or retrieve from an empty queue.ConcurrentMap
is a subinterface ofjava.util.Map
that defines useful atomic operations. These operations remove or replace a key-value pair only if the key is present, or add a key-value pair only if the key is absent. Making these operations atomic helps avoid synchronization. The standard general-purpose implementation ofConcurrentMap
isConcurrentHashMap
, which is a concurrent analog ofHashMap
.ConcurrentNavigableMap
is a subinterface ofConcurrentMap
that supports approximate matches. The standard general-purpose implementation ofConcurrentNavigableMap
isConcurrentSkipListMap
, which is a concurrent analog ofTreeMap
.All of these collections help avoid Memory Consistency Errors by defining a happens-before relationship between an operation that adds an object to the collection with subsequent operations that access or remove that object.