New

[Alex Buckley]

The draft spec in the OpenJDK Lambda project will continue to avoid 
'new' in the denotation of a lambda expression.

Let me remind everyone that a spec from this project is likely to be 
merely a starting point for a JSR Expert Group. The Expert Group members 
may or may not review the mailing list archives of this project, so 
endless syntax discussions here are somewhat futile. Before anyone asks, 
I have no information about the formation or schedule of such a JSR.

Alex

On 3/29/2010 2:36 AM, Howard Lovatt wrote:
> A number of people have commented about using new for lambdas, there are at
> least 4 good reasons to use new:
> 
> 1. It is what the rest of Java uses, e.g.:
> 
>   List<Integer> list = new ArrayList<Integer>();
>   #<int()> lambda = new #<int()>(42);
> 
> 2. It is compatible with the diamond operator from Coin (assuming <> are
> used), e.g.:
> 
>   List<Integer> list = new ArrayList<>();
>   #<int()> lambda = new #<>(42);
> 
> 3. The main argument for not using new is that the compiler can 'lift' the
> lambda to be static if it doesn't access any instance fields or local
> variables. However this type of optimization has a poor history in Java,
> think String interning and copying of static fields. In Java a JVM
> optimization has proven much more successful than a compiler optimization.
> Hence using new, which would allow a JVM optimization but prevent a compiler
> optimization, is the best choice.
> 
> 4. There are times when you want to control instantiation, consider a GUI
> application that uses a custom queue that checks for double entries (e.g.
> caused by an impatient user multiply single clicking - I do this!), the job
> queue might be:
> 
>   class Jobs extends LinkedBlockingDeque< #<void()> > {
>     @Override public void put( final #<void()> e ) {
>       if ( !peekLast().equals( e ) ) { super.put( e ); }
>     }
>   }
> 
> Then you might implement the main class of an application as:
> 
>   class GUI {
>     private static final Jobs jobs = new Jobs();
> 
>     private static final #<int()> FRAME_TO_FRONT = new #<> { ... };
>     static void frameClicked() { jobs.put( FRAME_TO_FRONT ); }
> 
>     static void fileMenuClicked() {
>       final #<void()> toggleFileMenu = new #<> { ... };
>       jobs.put( toggleFileMenu );
>     }
> 
>     ...
>   }
> 
> Note how control over creation is critical, multiple frameClicked() calls
> can be safely eliminated but multiple fileMenuClicked() calls cannot because
> these toggle the menu.
> 
>  -- Howard.
> 
> PS # could be substituted for lambda, Lambda, Function, etc.
>