From: Greg McIntyre <greg@...>
Date: 2005-09-07T10:46:29+09:00
Subject: Re: ruby style blocks in java

On Wed, 07 Sep 2005 02:36:28 +1000, Martin Ankerl  
<martin.ankerl@gmail.com> wrote:

> Is there a nice way to implement Ruby-style blocks in Java? I have to  
> code in Java and I really miss this feature. This is the best thing I  
> came up with, but it is soooo verbose (untested, just from my head):
>
> interface Block {
>    public Object yield(Object o);
> }
>
> class Array {
>    public void do(Block b) {
>      // do something here
>      while (it.hasNext()) {
>        Object o = it.next();
>        block.yield(o);
>     }
> }
>
> class Someth
>    public void doSomething() {
>      Array a = new Array();
>      // do something before
>      a.do(new Block() {
>        public void yield(Object o) {
>          // here is the yield code
>        }
>      }
>      // do something afterwards
>    }
> }
>

 From my experience attempting exactly the same, that's as close as I could  
get too (using final 1-element arrays to write back to the block's calling  
context). I also ran across Groovy. There's also jruby but I haven't  
really tried either.

I also found it better to stick the interface inside the class that uses  
it and name it after the method that uses it. Exception handling can also  
be a PITA with this kind of thing.

Despite being verbose, the sort of thing you have above actually cut down  
the number of lines of Java code I had to write by factoring out a whole  
lot of JDBC try/finally code. If you hunt around for the recommended way  
of using JDBC you'll see there are about 6 lines inside a finally clause  
that involve cleaning up the record set and statement objects.

The main problem I found though is that all those Java standard libraries  
simply don't use blocks, so they're only good for things you implement  
yourself.

-- 
Greg McIntyre