Marker interface pattern: Difference between revisions

Revision as of 10:48, 4 January 2011

Revision as of 13:12, 23 January 2011

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To use this pattern, a [[Class (computer science)|class]] implements a '''marker interface''', and methods that interact with instances of that class test for the existence of the interface. Whereas a typical [[interface (computer science)|interface]] specifies functionality (in the form of method declarations) that an implementing class must support, a marker interface need not do so. The mere presence of such an interface indicates specific behavior on the part of the implementing class. Hybrid interfaces, which both act as markers and specify required methods, are possible but may prove confusing if improperly used.

An example of the application of marker interfaces from the [[Java (programming language)|Java programming language]] is the {{Javadoc:SE|java/io|Serializable}} interface. A class implements this interface to indicate that its non-[[Transient (computer programming)|transient]] data members can be written to an {{Javadoc:SE|java/io|ObjectOutputStream}}. The <code>ObjectOutputStream</code> private method <code>writeObject()</code> contains a series of <code>instanceof</code> tests to determine writeability, one of which looks for the <code>Serializable</code> interface. If noneany of these tests passfails, the method throws a <code>NotSerializableException</code>.

== Critique ==