Lots of static methods in an interface

[Brian Goetz]

Yes, we already tried this.  And found (to our chagrin and shock) that 
there was class in the JDK that implements List and Set, which blows 
this strategy up.  And that fixing this would be prohibitively 
difficult, because its also Serializable and therefore we had to worry 
about serialization compatibility (you can't make this stuff up.)

On 9/11/2013 7:46 AM, Daniel Latrémolière wrote:
>
>> Right.  More generally, there are things to love about this approach (no
>> garbage side-classes, fewer "magic" place(s) to look for relevant static
>> methods), and things to worry about (messing up the interface with lots
>> of methods of varying relevance.)  I think we should embrace both the
>> love and the worry.
>>
>> In reality, I think the two poles -- the "old way" (put everything in a
>> side class) and "put everything in the interface" are both probably
>> excessive extremes.  The poster child for this tension is Collections;
>> do we really want *all* of these methods in Collection?  Some are pretty
>> esoteric.
> Some methods can also be merged by becoming default methods and using
> override of return type. By example, all unmodifiable*, synchronized*,
> checked* methods can become only three default methods:
>
> |public interface Collection<E> {||
> ||
> ||    public default Collection<E> asUnmodifiable() {||
> ||        return Collections.unmodifiableCollection(this);||
> ||    }||
> ||||
> ||    public default Collection<E> asSynchronized() {||
> ||        return Collections.synchronizedCollection(this);||
> ||    }||
> ||||
> ||    public default Collection<E> asChecked(Class<E> type) {||
> ||        return Collections.checkedCollection(this, type);||
> ||    }||
> ||||
> ||}||
> ||
> ||public interface List<E> {||
> ||||
>      @Override
> ||    public default List<E> asUnmodifiable() {||
> ||        return Collections.unmodifiableList(this);||
> ||    }||
> ||||
> |||||    @Override
> |||    public default List<E> asSynchronized() {||
> ||        return Collections.synchronizedList(this);||
> ||    }||
> ||||
> |||||    @Override
> |||    public default List<E> asChecked(Class<E> type) {||
> ||        return Collections.checkedList(this, type);||
> ||    }||
> ||||
> ||}|
>
> etc. for each collection specializing its return type as itself.
>
> Daniel.