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I was refactoring some java to use decorators. All of the decorators inherited from a class ThingDecorator, let's say. This consisted entirely of:

SomeType methodName(OtherType otherThing) {
    return decoratedObject.methodName(otherThing);
}

For maybe 20 methods of that form. This is like writing "this thing is a decorator" over and over again, which just drives me nuts as a DRY enthusiast. Every addition to the activities of this class needs an addition to the class[es] that form the basic un-decorated behavior and the decorator, but it's always just "this thing is still a decorator!" all over again. Is there any way to express once that an object is to delegate all non-overridden methods to some member field?

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  • You might be able to do it with a compile time annotation, not certain. However, even if you could, it would confuse IDEs something horrible.
    – user40980
    Nov 28, 2015 at 3:38
  • Unless the base decorator is a class stating the contract, I see no reason why you would want to inherit from it, you might as well just use an interface. This seems like a violation of LSP.
    – Andy
    Nov 28, 2015 at 7:10
  • @davidpacker for the purpose of the question it doesn't matter, but the real project had an interface AbstractThing that was the contract, a BasicThing implements AbstractThing that was the default behavior of a Thing, a ThingDecorator implements AbstractThing whose only task was to have a reference to an AbstractThing and delegate all calls to it, a plethora of ThingWithSomeStuff extends ThingDecorator which provided only the concrete meaning of the Thing having some Stuff, and finally a ThingToPointAt for hiding the decoration from things that don't know they need it.
    – sqykly
    Nov 28, 2015 at 13:02
  • @davidpacker (cont) in the more complete picture, it should be clear that both levels of abstract hierarchy are puposeful - the interface defines the contract, the BasicThing fulfills the contract provided by the interface, the abstract base decorator ensures that any concrete decorator that doesn't fulfill the entire contract has a reference to a thing that can and uses it to do so without needing to understand the entire contract of a Thing when all you want is for it to have some Stuff.
    – sqykly
    Nov 28, 2015 at 13:32
  • @davidpacker final clarification because that sounds overcomplicated otherwise: there were many different kinds of Stuff that could affect a Thing and many different kinds of Thing, and new kinds of Stuff were being added with every revision. Before I got there, all Stuff had to be defined, considered, and managed throughout the Thing that it affected. It was already quite complicated, my way is actually a lot neater.
    – sqykly
    Nov 28, 2015 at 13:55

1 Answer 1

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No, unfortunately, there isn't any way to accomplish this.

Unless you use some magic, like this: michael.gr - Intertwine: Normalizing Interface Invocations (which though I have implemented for C#, not for Java yet.)

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  • I hover around the use of magic (technically I guess it's code generation or macros, though we don't like using the word anymore thanks to C) and hesitate because I worry that no one will ever be able to just pick up my code and read it knowing plain old java. Right after I wrote this question, I wrote a sweet.js macro for it, but I just know that as dry and beautiful as it is, I can never use it in a serious project. Depressing.
    – sqykly
    Nov 28, 2015 at 4:05
  • I am giving the question a little more time, but I am not forgetting a check mark for the "there is no answer" answer if no one can come up with some miracle.
    – sqykly
    Nov 28, 2015 at 6:36

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