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copied!<p>I don't really think the problem is setter vs. constructor injection. The problem is you're using <code>null</code> to mean too many things...</p> <p>As for : <code>/* A null value should create a unique meaningful default */</code></p> <p>Using it as a "magic" value in the <code>setId()</code> method is also something that really seems like a bad code smell. If you never call <code>setId()</code> then <code>getId()</code> returns <code>null</code>, but if you call <code>setId(null)</code> then <code>getId()</code> returns some generated value?</p> <p>Something like this would seem to make more sense:</p> <pre><code>public abstract class MyIdentityBaseClass implements IMyIdentityInterface { private String _id; private IMyIdentityInterface _parent; public MyIdentityBaseClass () {} @Override public String getId() { return _id; } @Override public void setId(String id) { _id = id; } @Override public IMyIdentityInterface getParent() { return _parent; } @Override public void setParent(IMyIdentityInterface parent) { _parent = parent; if (_id == null) { // if id isn't already set, set it to the generated id. _id = Helpers.makeIdFromParent(parent, getClass()); } } } </code></pre> <p>If your model really requires a parent feel free to use constructor injection, that's what it's there for. But realize you're still going to have to provide a default constructor for top level items... and then what's to stop someone from using the default constructor for an item that's not top level and then call <code>setParent()</code> on it later. I'd look at creating some kind of Container/Component architecture and make a special class (or classes) for the top level items. (You may have this already, as you've only given one example class and an abstract one at that.)</p> <p>BTW - Also, the IInterface and _name conventions aren't Java naming conventions. If this is an exposed API that other people are supposed to use expect some complaining.</p>

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