Re: forEach and Casting

On Apr 22, 3:54 pm, Tom Hawtin <use...@xxxxxxxxxxxxxxxxx> wrote:
Jason Cavett wrote:

Currently, the collection I'm using an Iterator over contains objects
of a Generic type (an abstract class). When I get the object from the
collection, I must cast it to the more specific type so I can use the
various methods. There is no way to change this.

I suggest you really make sure whether you can change it or not. If you
are using generics, casts often mean design issues.

// this is the part I'm not sure about - can I even do something like
this?
for(Specific o : (Specific) genericCollection) {

You can quite easily make a "safe" casting iterator.

/**
* <strong>{see Iterator#next}
* will throw ClassCastException...</strong>
*/
public static <T> Iterable<T> castIterable(
final Class<T> clazz, final Iterable<? super T> iterable
) {
return new Iterable<T>() {
public java.util.Iterator<T> iterator() {
return new java.util.Iterator<T>() {
private final java.util.Iterator<? super T> target =
iterable.iterator();
public boolean hasNext() {
return target.hasNext();
}
public T next() {
return clazz.cast(target.next());
}
public void remove() {
target.remove();
}
};
}
};
}

...
for (Specific thing : castIterable(Specific.class, generals)) {

(Disclaimer: Not tested.)

Tom Hawtin

Well, the reason it can't easily be changed is because I don't know
what class I'm going to want until runtime. It depends on where the
user is at in the tree structure since each component in the tree is
different (even though they all have the same superclass).

As such, I need a class that can return the class type I want.

.

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