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New Refactoring for OT/J: Change Method Signature

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IDE Innovation

Every now and then some folks report that the IDE they’re developing now supports this or that cool new feature. Sometimes I envy them for such progress – but more often than not I end up realizing that the OTDT already has that feature or something very similar. Is that just my personal bias (which certainly I have) or are we cheating in some way, or what?

There’s a little detail in the design of the OTDT that turns out to make such a difference as normally can only achieved by cheating: by the way how the OTDT extends and adapts the JDT it is like saying we’re starting the race not at the line saying “START” but at the other one saying “FINISH” and run on from there. While many projects define “JDT-like user experience” as their long-term goal, the OTDT basically has this since the first release. How come? The OTDT basically is the JDT, with adaptations.

There’s a fine point in the word basically. To tell the truth, every feature that the JDT supports for Java development is not automatically fully available in the OTDT for OT/J development. In fact most JDT features need adaptation to provide equal convenience for OT/J development. It’s just that all these adaptations can be brought into the system very very easily – thanks to the self-application of OT/Equinox. And now, here is actually an example of a JDT feature that lacked OT/J support – until yesterday:

Change Method Signature Refactoring

If you refactor mercilessly the “Change Method Signature” refactoring is certainly one of your friends. Add/rename/remove/reshuffle parameters of a method without (too easily) breaking existing code, cool. It knows about the connections from method invocation to method declaration and about overriding. That’s good enough for Java, but not good enough for OT/J since OT/J introduces method bindings (“callout” and “callin”) that create a wiring between methods of different objects. Obviously, if one of the methods being wired changes its signature so must the method binding.

Technically, the JDT implementation of that refactoring bailed out when it asked a parameter/argument for its parent in the AST and found neither a method declaration nor a method invocation. The JDT refactoring does not know about OT/J method bindings, so it just failed to update those.

After a little of coding this is what happens now when you apply “Change Method Signature” on a piece of OT/J code. Assume you have a plain Java class:

public class BaseClass {
        public void bm(int i, boolean b) {
        void other() {
                bm(3, false);

and a TeamClass whose contained RoleClass is bound to BaseClass:

public team class TeamClass {
        protected class RoleClass playedBy BaseClass {
                void rm(int i2, boolean b2) <- after void bm(int i, boolean b);
                private void rm(int i2, boolean b2) {

Here the right-hand side of the callin binding in line 4 refers to the normal method bm(int,boolean) defined in BaseClass.

What happens if you start messing around with the signature of bm?

Change Singature - Edit Parameters

I.e., we are adding a parameter str and also change the order of parameters (from i,b to b,str,i). I don’t have to tell you what this refactoring does to BaseClass, but here’s the preview of those changes affecting TeamClass:

Change Signature - Preview TeamClass

(sorry the screenshot is a bit wide, you may have to click to really see).

The preview shows that the refactoring will do three things:

  1. Update the right-hand side of the method binding.
  2. Add a parameter mapping (the part starting with “with“) to ensure that the role method rm receives the arguments it needs, the way it needs them.
  3. Do not update any part of the role implementation, because that’s what the parameter mapping is for: shield the role implementation from any outside changes.

Some words on these parameter mappings: each element like “b2 <- b” feeds a value from the right-hand side (representing things at the baseclass side) into the parameter at the left-hand side (representing the role). The list of parameter mappings is not ordered, which means further swapping of base side parameters requires no further action. And indeed the current implementation of the refactoring does not attempt to adjust an existing parameter mapping (which might be a quite complex task). If adjustments are required which the refactoring cannot perform automatically, it will inform the user that perhaps a parameter mapping may need manual adjustment.

The refactoring applies no AI to guess what the intended solution should look like, but it performs a number of obvious adaptations and gives note when these adaptations may not suffice and manual cleanup may be needed.


Those who have read previous posts may (almost) know the kind of statistics that follows:

  • 299 LOC implementation
  • 315 LOC testcode
  • 170 LOC testdata

I should really show one of these OT/J based implementation, one of these days. For this post I will just give you an Outline, literally:
Implementation Outline

Role class Processor is bound to the JDT’s ChangeSignatureProcessor, and the nested roles OccurrenceUpdate and MethodSpecUpdate are bound to two inner classes of ChangeSignatureProcessor, which shows how even class nesting at the base level can be mapped to the team & role level. Instances of the innermost roles will only ever come into being, if a Processor role has detected that it needs to work in order to handle OT/J specific code. Inside each role – apart from regular fields and methods – you see those green arrow-things, denoting method bindings between a role and its base. The highlighted binding to createOccurrenceUpdate is actually the initial entry into the logic of this module. Further down you see how the base behavior reshuffleElements is intercepted to additionally add parameter mappings if needed (and yes, I’m hiding the details of role MethodSpecUpdate, but there are no secrets inside, I just more methods and more method bindings).

Voilà, we indeed have a new refactoring for OT/J. I’ve been planning this one for a while but in the end it took me little more than a day 🙂


Written by Stephan Herrmann

August 29, 2010 at 20:52

Posted in Eclipse, Object Teams, OTDT, OTEquinox

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