Sized (original) (raw)

Brian Goetz brian.goetz at oracle.com
Fri Nov 2 15:05:33 PDT 2012

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We've been using a placeholder interface Sized in the Streams API, for two reasons:

• It is useful to indicate that an aggregate knows its size (Collections do, but not all Iterables do, and we've taken advantage of this in the Streams library)
• It provides a piece of the story for the migration to 64-bit collections.

Here's how this migration story might work. Today, we have:

interface Sized { int size(); default long longSize() { return size(); } }

and add it as a new supertype of Collection.

Then (now or later) we can add a subtype:

interface LongSized extends Sized { default int size() { long size = longSize(); if (size > Integer.MAX_VALUE) throw something; return (int) size; }

 long longSize(); // reabstraction

}

Then, 64-bit-aware collections can implement LongSized.

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