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PODesign pattern for default implementation with empty methods
 

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    <p>Is there a specific <strong>design pattern</strong> that describes the scenario where a non-abstract default implementation is provided that implements all or some of the methods on the interface with empty, NO-OP implementations. This being done with the intent of alleviating subclasses with the burden of implementing methods that they themselves may not need/use:</p> <pre><code>public interface MyInterface { public void doThis(); public void doThat(); public void done(); } public class MyClass implements MyInterface { public void doThis() { // NO-OP } public void doThat() { // NO-OP } public void done() { // Some standard implementation } } public class MuSubClass extends MyClass { public void doThat() { // Subclass only cares about doThat() } } </code></pre> <p>I have seen this pattern used a number of times including <a href="https://docs.oracle.com/javase/8/docs/api/org/xml/sax/helpers/DefaultHandler.html" rel="noreferrer">Java's DefaultHandler in the SAX framework</a>, and <a href="https://docs.oracle.com/javase/8/docs/api/java/awt/event/MouseAdapter.html" rel="noreferrer">MouseAdapter</a>. In somes cases such classes are named as Adaptors, but I was under the impression that the adapter pattern translates between two different interfaces. </p> <p>Given that in these instances there is only one declared interface that is being translated to an undefined subset of that interface - I am not clear on how this is in the spirit of the adapter pattern.</p> <p>Furthermore, I don't quite see how this adheres to the <a href="http://en.wikipedia.org/wiki/Null_Object_pattern" rel="noreferrer">NullObject pattern</a> either, given that some methods could have an implementation, and the NullObject is traditionally a singleton.</p>
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    1. USGreg Chabala
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    1. COI agree that this is neither Null Object or Adapter. Don't know what to call it, though.
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      1. USKristopher Johnson
 

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