Sized

[Doug Lea]

Sorry for the delay on this...

On 11/05/12 18:48, Brian Goetz wrote:
> The real purpose is as I specified earlier -- providing a migration path for the
> 32-bit size limitation that is hard-coded into Collections.  There are a number
> of size-like methods in new APIs and I want to select neither of the following
> signatures:
>
>    int size()
>    long size()
>
> Instead, I want to make a choice based on a framework for migration towards
> 64-bit collections.  The Sized I proposed was one possible way to do this in an
> organized way.

On looking at this, I'm not seeing the migration path under the current
interface. First, it is not clear that Collection can extend size:

public interface Sized {
     /**
      * A non-negative integer indicating a count of elements for this object.
      */
     int size();

     default boolean isEmpty() { return size() == 0; }
}

But Collection.size says:

     /**
      * Returns the number of elements in this collection.  If this collection
      * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
      * <tt>Integer.MAX_VALUE</tt>.
      *
      * @return the number of elements in this collection
      */
     int size();

And all(?) JDK classes in which the element count can overflow do
report Integer.MAX_VALUE. In other words, greater-than-int-sized
collections are not a future possibility, but a reality that
was a few years the subject of several collections bugfixes.
That will also require stream bugfixes soon enough.

I still think the only way out is to introduce a new method
with long return type. We could even do it while keeping the name
Sized, but leaving the size() method alone for continued use in
Collections-only applications, and defaulting the new method in
Collection:

public interface Sized { // or pick a new name
     /**
      * Returns the number of elements
      */
     long elementCount(); // oh no, another arbitrary name choice

     default boolean isEmpty() { return elementCount() == 0; }
}

interface Collection<E> extends Sized ... {
   default long elementCount() { return (long)size(); }
   ...
}