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This example could be implemented with the Java 8 merge() but it shows the overall lock-free pattern, which is more general. This example is not related to the internals of the ConcurrentMap but to the client code's use of the ConcurrentMap. For example, if we want to multiply a value in the Map by a constant C atomically:
The following is an example of a class with lazy initialization implemented in ... import java.util.Map; import java.util.Map.Entry; ... types. entrySet ()) ...
The object pool design pattern is used in several places in the standard classes of the .NET Framework. One example is the .NET Framework Data Provider for SQL Server. As SQL Server database connections can be slow to create, a pool of connections is maintained. Closing a connection does not actually relinquish the link to SQL Server.
Apache Cayenne, open-source for Java; Apache OpenJPA, open-source for Java; DataNucleus, open-source JDO and JPA implementation (formerly known as JPOX) Ebean, open-source ORM framework; EclipseLink, Eclipse persistence platform; Enterprise JavaBeans (EJB) Enterprise Objects Framework, Mac OS X/Java, part of Apple WebObjects
The goal of the pattern is to keep the in-memory representation and the persistent data store independent of each other and the data mapper itself. This is useful when one needs to model and enforce strict business processes on the data in the domain layer that do not map neatly to the persistent data store. [2]
For example, consider an address book entry that represents a single person along with zero or more phone numbers and zero or more addresses. This could be modeled in an object-oriented implementation by a "Person object " with an attribute/field to hold each data item that the entry comprises: the person's name, a list of phone numbers, and a ...
Map functions can be and often are defined in terms of a fold such as foldr, which means one can do a map-fold fusion: foldr f z . map g is equivalent to foldr (f . g) z. The implementation of map above on singly linked lists is not tail-recursive, so it may build up a lot of frames on the stack when called with a large list. Many languages ...
The implementation of the idiom relies on the initialization phase of execution within the Java Virtual Machine (JVM) as specified by the Java Language Specification (JLS). [3] When the class Something is loaded by the JVM, the class goes through initialization. Since the class does not have any static variables to initialize, the ...