Design pattern for default implementation with empty methods

Question

Is there a specific design pattern 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:

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()
    }
}

I have seen this pattern used a number of times including Java's DefaultHandler in the SAX framework, and MouseAdapter. In somes cases such classes are named as Adaptors, but I was under the impression that the adapter pattern translates between two different interfaces.

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.

Furthermore, I don't quite see how this adheres to the NullObject pattern either, given that some methods could have an implementation, and the NullObject is traditionally a singleton.

Answer 1

There are no design patterns for default implementation.

I usually append DoNothing prefix to the name of class. Depending on it's intent I use also Base or Default (the latter is widely used). Probably MouseAdapter should be called DefaultMouseListener.

In the case you care, you can stub systematically an interface with a simple DynamicProxy, you must return only a "nice" default value (null for Object, 0 for numeric, etc).

BTW this is a very good question.

EDIT

Furthermore this is neither a Stub or a Mock: maybe it can be confused with a Stub but the intent is different.

Answer 2

You should follow different design principle : interface-segregation principle

The Interface Segregation Principle states that clients should not be forced to implement interfaces they don't use. Instead of one fat interface many small interfaces are preferred based on groups of methods, each one serving one sub module.

You should not implement MORE And you should not implement LESS

Have a look at related SE questions for more details.

The Interface Segregation Principle

Interface Segregation Principle- Program to an interface

Answer 3

I have seen this design used in spring where they have a class named FlowExecutionListenerAdapter which saves you implementing all the FlowExecutionListener operations.

However, it does sound like the Null Object Pattern too. However I feel it sits better in the Adapter world purely because it changing the behavour of the interface by allowing you only to implement the bit you want...but its a tough one.

I'm sure this question has been asked before?

This sounds similar no? might be worth a read.