I am currently having to bend some framework API to fit my usecase. The framework provides generic interfaces such as

public interface Processor<T> {
    T process(T t);

with various implementations. These are used by some classes such as

public SomeClass<T> {
    public SomeClass(Processor<T> p, [...]) {}

To fit my usecase, I need SomeClass to behave differently without affecting the existing Processors. To do so, SomeClass has to operate on wrapped Ts. Hence:


As said, this should not affect the Processors which still shall operate on T. To be able to do this I wrote delegators which unwrap T from the container and then delegate the processing of T:

public class BoxDelegatingProcessor<T> implements Processor<Container<T>> {
    private Processor<T> delegatee;

    public Container<T> process(Container<T> wrapped) {
        return wrap(delegatee.process(unwrap(wrapped));

What design pattern (according to GoF) is this? I don't think it's Decorator, because there es no actual "functionality" involved? It's more of a type adapter.

  • This one sounds like decorator pattern – Low Flying Pelican Feb 27 '15 at 21:53
  • I don't know what GoF pattern this is. But to me it looks like the purpose of the Processor interface is as follows: Process takes a T and returns a T, so it is possibly manipulating it in some way. The purpose of passing a Processor interface to the SomeClass constructor is to be able to change the behavior of the processing WITHOUT NEEDING TO CHANGE SOMECLASS. Instead, you would just create a new class that implements the process method. I'm a little confused at what your BoxDelegatingProcessor is attempting to do. – public wireless Feb 28 '15 at 0:36
  • Also, are you sure you need SomeClass<Container<T>>? Could you not create a List or Array of SomeClass<T> ?? – public wireless Feb 28 '15 at 0:38
  • 2
    The GOF patterns are not comprehensive. There's no guarantee that any particular technique is covered by GOF. – Robert Harvey Feb 28 '15 at 2:19

This is the adaptor pattern. You are adapting a Processor<T> so it can be used where a Processor<Container<T>> is expected.

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