StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<blockquote> <p>The first associative collection class to appear in the Java class library was Hashtable, which was part of JDK 1.0. Hashtable provided an easy-to-use, thread-safe, associative map capability, and it was certainly convenient. However, the thread-safety came at a price -- all methods of Hashtable were synchronized. At that time, uncontended synchronization had a measurable performance cost. The successor to Hashtable, HashMap, which appeared as part of the Collections framework in JDK 1.2, addressed thread-safety by providing an unsynchronized base class and a synchronized wrapper, Collections.synchronizedMap. Separating the base functionality from the thread-safety Collections.synchronizedMap allowed users who needed synchronization to have it, but users who didn't need it didn't have to pay for it.</p> <p>The simple approach to synchronization taken by both Hashtable and synchronizedMap -- synchronizing each method on the Hashtable or the synchronized Map wrapper object -- has two principal deficiencies. It is an impediment to scalability, because only one thread can access the hash table at a time. At the same time, it is insufficient to provide true thread safety, in that many common compound operations still require additional synchronization. While simple operations such as get() and put() can complete safely without additional synchronization, there are several common sequences of operations, such as iteration or put-if-absent, which still require external synchronization to avoid data races.</p> </blockquote> <p>The following link is the source and has more information: <a href="http://www.ibm.com/developerworks/java/library/j-jtp07233/index.html" rel="nofollow">Concurrent Collections Classes</a></p>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload