When dealing with APIs that return Collection of /SomeClass/
instances, you need to dig into the source code to figure out what
to cast the retrieved value to (unless the API doc explains it :)
Creating custom collections by delegation to standard collections
seems to be a simple solution to this problem.
To illustrate with code:
/*
* Lets say I return a List of MyThing objects, I could write a
* CustomList that is backed by a std List as:
*/
<code>
public class MyThingList {
public MyThing get(int index) {
(MyThing) internalList.get(index);
}
public void add(MyThing thing) {
internalList.add(thing);
}
public MyThingIterator iterator() {
return new MyThingIterator(internalList.iterator());
}
// do the other List methods, you get the idea
/*
* CustomIterator that delegates to std iterator
*/
public static class MyThingIterator {
public MyThingIterator(Iterator iter) {
internalIterator = iter;
}
public MyThing next() {
return (MyThing) internalIterator.next();
}
// do the other iterator methods, you get the idea
}
}
</code>
The disadvantages:
- Will have to write a class for every Map/Set/List/Collection
that we use.
- Cannot switch Map/List.. implementations easily (Like use
HashSet instead of TreeSet as the underlying collection)
The advantages are:
- Self Explanatory API (to some extent)
- No need of casting in code that uses the API: Better static checking
- Could be made into an eclipse plugin (atleast in theory)
... which counters the first disadvantage to an extent.
I would imagine that this is similar to what the Generics
should be doing behind the scenes, with the advantage ofcourse
that you dont have to write the custom collection class - the
compiler generates it for you.
Still, in "JDK < 1.5" simulating generics seems to be worthwhile
(heck, we could even have an eclipse plugin that generates
the simulator class)
I dont imagine I am the first to come across the problem or
this solution - AND - I have never used this approach myself :)
So i would like to have comments or criticism of this approach
from others:
- is this a fairly common solution?
- are there some known problems with this approach?
- the disadvantages outweigh the advantages because....
etc.
~ amol
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