Unmodifiable child collections

mate · **Posted:** Tue Dec 21, 2004 4:11 am

I'm currently reading the reference manual and have some thoughts considering the parent/child model in chapter 9 (version 2.1.1). I want to use the principles in the example (9.2), but I also want to make sure nobody adds a child without calling addChild() but instead getChildren().add() - and thus possibly not setting the parent. Therefore I am thinking I would modify getChildren() to return an unmodifiable Set instead.

Code:

public class Parent {
  ...
  private Set children
  ...

  public Set getKittens() {
      return java.util.Collections.unmodifiableSet(kittens);
  }

  public void addChild(Child c) {
    c.setParent(this);
    children.add(c);
  }
}

For the mapping to work properly, I assume I need to set

Code:

access="field"

on the property. (access="field" works for private properties, right?)

Would this generally be a good idea?
Could it cause any problems with lazy initialization?

max · **Posted:** Tue Dec 21, 2004 5:18 am

i haven't tried it, but i don't think it would be a good idea!

Instead don't have the getChildren public (make it private) or simply as you say use field access to protect it.

mate · **Posted:** Tue Dec 21, 2004 5:24 am

max wrote:

Instead don't have the getChildren public (make it private) or simply as you say use field access to protect it.

So then how would the rest of the application access the children (for reading)???
Through a getUnmodifiableChildren() with the abovementioned implementation? What would be the difference to using field mapping?

mate · **Posted:** Tue Dec 21, 2004 5:27 am

mate wrote:

Code:

public Set getKittens() {
      return java.util.Collections.unmodifiableSet(kittens);
  }

This should of course read

Code:

public Set getChildren() {
      return java.util.Collections.unmodifiableSet(children);
  }

(I obviously mixed two examples)

max · **Posted:** Tue Dec 21, 2004 6:35 am

just map it as access="field" and you can have whatever getter you want.

mate · **Posted:** Tue Dec 21, 2004 6:43 am

max wrote:

just map it as access="field" and you can have whatever getter you want.

That was my initial thought, which you said wasn't a good idea.
I'm sorry, but I just don't follow...

max · **Posted:** Tue Dec 21, 2004 6:56 am

oh sorry - i answered to fast.

I just noticed the concurrent sets, not the access="field" - my bad ;)

just do it then ;)