Will JDK 8 support SAM that is Abstract Class ?

[Remi Forax]

On 11/05/2012 04:08 PM, Boaz Nahum wrote:
> Does it mean that all 'old' inner classes extending adapters cant be
> converted to lambda(assuming converting the adapter to SAM)?
> Please say no: (

We drop that support because an abstract class has a constructor (at 
least one)
that can observe the creation of the lambda so it defeat most of the 
optimizations
that the VM can do.

The other problem was to deal with abstract class with a constructor 
that may throw an exception
because again, the construction of the lambda is observable.

You can still retrofit your code to use lambda using delegation instead 
of inheritance.
By example:

abstract class Foo<T> {
   Foo() {
      // some side effects
   }
   public abstract void m(T element);
}

Foo<String> foo = new Foo<String>() {
   public void m(String s) {
     // lambda code
   }
};

can be retrofitted to:

class Foo<T> {
   private final Block<? super T> block;
   Foo(Block<? super T> block) {
      this.block = block;
      // some side effects
   }
   public void m(T element) {
     block.apply(element);
   }
}

Foo<String> foo = new Foo<String>((String s) -> {
   // lambda code
});


>
> Thanks
> Boaz

Cheers,
Rémi

> On Nov 5, 2012 5:01 PM, "Reinier Zwitserloot" <reinier at zwitserloot.com>
> wrote:
>
>> It was part of the original plan, but I believe non-interface SAMs have
>> been dropped. I'm guessing because it was difficult to handle the peculiars
>> of working with MethodHandles and not actually making a new instance of the
>> SAM type.
>>
>>   --Reinier Zwitserloot
>>
>>
>>
>> On Mon, Nov 5, 2012 at 3:41 PM, Boaz Nahum <boaznahum at gmail.com> wrote:
>>
>>> I can't find what the spec is saying, but I remember that Abstract class
>>> with one abstract method is also SAM.
>>>
>>> Currently in b63 I got java: incompatible types: the target type must be a
>>> functional interface
>>>
>>> Will it be supported in the future ?
>>>
>>> Thanks
>>> Boaz
>>>
>>>