Question

I’ve just come across a pattern I’ve seen before, and wanted to get opinions on it. The code in question involves an interface like this:

public interface MyCrazyAnalyzer {     public void setOptions(AnalyzerOptions options);     public void setText(String text);     public void initialize();     public int getOccurances(String query); } 

And the expected usage is like this:

MyCrazyAnalyzer crazy = AnalyzerFactory.getAnalyzer(); crazy.setOptions(true); crazy.initialize(); Map<String, Integer> results = new HashMap<String, Integer>(); for(String item : items) {     crazy.setText(item);     results.put(item, crazy.getOccurances); } 

There’s reasons for some of this. The setText(…) and getOccurances(…) are there because there are multiple queries you might want to do after doing the same expensive analysis on the data, but this can be refactored to a result class.

Why I think this is so bad: the implementation is storing state in a way that isn’t clearly indicated by the interface. I’ve also seen something similar involving an interface that required to call ‘prepareResult’, then ‘getResult’. Now, I can think of well designed code that employs some of these features. Hadoop Mapper interface extends JobConfigurable and Closeable, but I see a big difference because it’s a framework that uses user code implementing those interfaces, versus a service that could have multiple implementations. I suppose anything related to including a ‘close’ method that must be called is justified, since there isn’t any other reasonable way to do it. In some cases, like JDBC, this is a consequence of a leaky abstraction, but in the two pieces of code I’m thinking of, it’s pretty clearly a consequence of programmers hastily adding an interface to a spaghetti code class to clean it up.

My questions are:

1. Does everyone agree this is a poorly designed interface?
2. Is this a described anti-pattern?
3. Does this kind of initialization ever belong in an interface?
4. Does this only seem wrong to me because I have a preference for functional style and immutability?

If this is common enough to deserve a name, I suggest the ‘Secret Handshake’ anti-pattern for an interface that forces you to call multiple methods in a particular order when the interface isn’t inherently stateful (like a Collection).

Answer 1

Yes, it’s an anti-pattern: Sequential coupling.

I’d refactor into Options – passed to the factory, and Results, returned from an analyseText() method.