Talk:FriendPackages

From APIDesign

Comments by Tim Band (TBa).

• TBa: Accessor could perhaps be called ItemAccessor (living in ItemAccessor.java)? This makes it more obvious that you have to write this boilerplate for each class needing the back door. TBa
• JST: Actually once per package is enough.

• TBa: It would be nice to be able to put in extra comments without cluttering up the text. Hovers would be ideal, but I guess not supported by this Wiki (and not in the code section anyway). Is there any way of doing footnotes?
• JST: This is wikipedia::mediawiki and it has a lot of extensions. More than I know about.

• TBa: The particular point is the line l = listener in Item.java. This is presumably so that in the presence of multiple threads, an "obsolete" listener may be called, but you will never get a null pointer exception. That's too much to clutter the code with, but it spent quite a bit of my effort working it out.
• JST: The current code is not really multithreaded.

• TBa: Should all the "default"s really be called "default"? aren't we really talking about TheAccessor or something?
• JST: I am not sure I get the comment, but NetBeans usually call singleton returning methods getDefault(). Having symmetrical setDefault(...) is appropriate, I guess.

• TBa: It is much clearer setting the DEFAULT directly than the book's indirect classloader method, but now shouldn't setDefault be synchronized?
• JST: The classloading trick is still there, I just moved it outside of the code snippets. It is only necessary if someone uses Accessor first without Item being loaded (e.g. which is only possible while calling constructor, I guess):

Code from Accessor.java:

private static final Class<?> INIT_API_CLASS = loadClass(
    Item.class.getName()
);
private static Class<?> loadClass(String name) {
    try {
        return Class.forName(
            name, true, Accessor.class.getClassLoader()
        );
    } catch (Exception ex) {
        throw new RuntimeException(ex);
    }
}
 

• 'JST': It might be possible to to put a guard in constructor of Accessor just like in this example:

Code from InterfaceThatJustJoeCanImplement.java:

public abstract class InterfaceThatJustJoeCanImplement {
    protected InterfaceThatJustJoeCanImplement() {
        if (!"impl.joe.JoesImpl".equals(getClass().getName())) {
            throw new IllegalStateException(
                "Sorry, you are not allowed to implement this class"
            );
        }
    }
 
    public abstract void everyoneCallThisJoeWillHandleTheRequest();
}