Multiton pattern

The multi-tone ( multi-tone English ) is a generation pattern is used for generating a specified number of objects. It is so to say an extension of the single piece, where only a single object is used. To access the correct object, a unique key is used. The objects and their keys are usually implemented as an associative array in the form of keys and values ​​that are delivered via a static method on request. Thus, there is at most one object is always for each key. If a key is specified for the object does not exist, the object required is generated and made available. Thus, a multi-tone is really nothing more than a group of individual pieces.

Example

A thread- safe Java implementation of a Multitons:

Java

Public class FooMultiton {          private static final Map instances = new HashMap ();            private FooMultiton () / * also acceptable: protected, {default } * / {              / * No explicit implementation * /          }            public static FooMultiton getInstance (Object key ) {              synchronized ( instances ) {                    / / Our "per key" singleton                  FooMultiton instance = instances.get ( key);                    if ( instance == null) {                        / / Lazily create instance                      instance = new FooMultiton ();                        / / Add it to map                      instances.put (key, instance );                  }                    return instance;              }          }            / / Other fields and methods ...        } Clarification of the example

In contrast to a hash table a multitone always returns an object; zero is therefore never returned. Clients can also specify a new key. It allows centralized access to a single directory. However, it goes in contrast with other solutions of the indicated storage ( such as LDAP ) on a single system.

Disadvantages

Unit testing a Multitons are difficult as in the single piece because global variables are used. It can also lead to memory leak if the language supports garbage collection.

Notes

Singleton pattern Variable (computer science) Design Patterns Factory method pattern Prototype pattern Decorator pattern Flyweight pattern Behavioral pattern Interpreter pattern Iterator pattern Memento pattern Template method pattern Strategy pattern Interceptor pattern Null Object pattern Data Access Object Dependency Injection Fluent Interface Inversion of Control Model–view–presenter Model View ViewModel
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