Java 8 Double function reference?

Question

Suppose I have this class:

class Dependency{      
   public Dependency reverse() { ... } // returns this Dependency after some reverse OP

   public int doSomething(int param) { ... }

}

Can I use it like this:

Optional<Integer> opt = ...
Dependency dep = new Dependency();

opt.map(dep::reverse::doSomething);

This would be quite clean, but is it possible? To apply a transformation (reverse) to Dependency and then apply the doSomething method?

"Can I use it like this" - no, this wont compile. Double-reference is not a thing. Maybe you intend to do two map calls. opt.map(...).map(...). Not exactly sure though what you are attempting to do here. It would help if you could show a working code snippet, even if it is not as elegant as you would like it to be. Just to understand your scenario. — Zabuzard
– Zabuzard, Commented Mar 17, 2020 at 18:19
You say (in the code comment) that reverse() modifies the Dependency instance? Then, why not change the declaration to Dependency dep = new Dependency().reverse();? — Holger
– Holger, Commented Mar 19, 2020 at 14:07

leo277 · Accepted Answer · 2020-03-17 18:29:02Z

6

If I understood you correctly, seems that reverse() won't be consuming the Integer, so you could simply do:

opt.map(dep.reverse()::doSomething);

answered Mar 17, 2020 at 18:29

leo277

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