I would add boilerplate getters/setters to the list. Almost always, a simple public field works just fine.
But I tend to err on the side of safety with my fields - private member, public accessors - while I work out my modeling and refactoring. When the design settles, then I can relax access if it's OK. And when something changes in the design (atomicity requirements, immutability, etc) I already have most of the boilerplate in place. Mostly though, I keep my accessors.
On a related note, do Java IDEs not provide boilerplate code? I'm more an Objective-C guy and the language now supports "here's a property" and "create the accessors" alongside my needs for custom ivar names, custom setters, etc. Even if Java the language doesn't have similar features, I'd expect IDEs to give you this kind of boilerplate stuff.
But generating getters and setters based on fields is putting the cart before the horse. You're right, it is very important for your classes to have a stable, clean public API that's distinct from the private implementation. But if that public API is intended to expose data at the field level, then just expose the fields without confusing the issue. If you don't want to expose the fields, then don't.
Having private-but-not-really fields with a lot of auto-generated getters and setters doesn't help you provide a clean, small API: instead, it bloats the public API. Also, it obfuscates what's actually happening... is a getter just a simple data value, or is it doing a bunch of complicated shit behind the scenes? And if it is doing a bunch of complicated shit, just make it a regular method on the public API, not a getter that's logically tied to a field that the client knows is there.
TL;DR: Fields are fields, methods are methods, auto-generating getters/setters blurs the line in unhelpful ways.
If you started out with getters/setters in the first place, you can do this without changing the API and ABI.
I would rather want a compile time error instead of a silently not changing value in a setter for example after a library upgrade
> That doesn't make a lot of sense. An API is an interface, which in this case exposes data. The fact that this data is held by objects at the field level as nothing to do with the purpose of the API: it's an implementation concern. The consumers of this API do not, and should not, need to know whether a field or anything else is used to provide the requested data. If the public API gets bloated when using getters/setters then blame Java, not this basic encapsulation principle.
is a getter just a simple data value, or is it doing a bunch of complicated shit behind the scenes?
> As you said, and as a rule of thumb, never do a bunch of complicated shit inside a getter: always expose a method for this operation. Just because getters exist does not mean methods should disappear.
Yes. The confusion comes from complecting[1] an object api and data. In general, having a class that is both a data structure (a bean or a struct) and a service class is a bad idea.
My contention is that if a class is Just Data, exposing public fields is fine. And if it is a service class that needs a consistent, stable API, it shouldn't be exposing fields via getters and setters either.
That's not really true in Java. The getter/setter pattern is baked into a lot of the standard Java libraries.
For example, Javabeans are:
a Java Object that is serializable, has a 0-argument constructor, and allows access to properties using getter and setter methods.[1]
Things like JPA, Jersey, Guice etc all rely on the Javabeans convention.
Yes, Java should have real properties like Object Pascal & C# does, but it doesn't, and getters & setters are harmless to anything except aesthetic sensibilities.
TL;DR: Getters & setters are a useful convention that allow many things that are not possible with public fields.
You can often customize this (it is Java after all!) but sometimes it's better to just go with the expected standard in the language.
Java rely needs properties...