Why does this() and super() have to be the first statement in a constructor?

[Ulf Zibis]

     class A extends Base {
         A() {
             // ERROR:
             Foo foo = new Foo();
             super(foo);
             foo.special_init();

              // Workaround: (would work, if we would have method invocation chaining:
              //                    
http://mail.openjdk.java.net/pipermail/coin-dev/2009-March/001180.html)
             super(__lastFoo.set(new Foo()).get());
             __lastFoo.get().special_init();
         }
         // Need to make it thread-local to avoid concurrent access.
         private static final ThreadLocal<Foo> __lastFoo = new ThreadLocal<Foo>();
     }

-Ulf


Am 08.10.2011 14:48, schrieb BODZ, Domain:
> +1, I've also had this problem for many times. Static helper doesn't always work, see this example:
>
>     class Base {
>         /* foo is private and unreadable, no getter anyway. */
>         private final Foo  foo;
>
>        Base(Foo foo) { this.foo = foo; }
>     }
>
>     class A extends Base {
>         A() {
>             // ERROR:
>                    Foo foo = new Foo();
>                    super(foo);
>                    foo.special_init();
>
>              // Workaround:
>                    super(__lastFoo = new Foo());
>                    Foo foo = __lastFoo;
>                    foo.special_init();
>         }
>         static Foo __lastFoo;    // XXX Need to make it thread-local to avoid concurrent access.
>     }
>
> -Xie Jilei
>
>
> On Sat, Oct 8, 2011 at 7:28 PM, Ulf Zibis <Ulf.Zibis at gmx.de <mailto:Ulf.Zibis at gmx.de>> wrote:
>
>     Anyway,
>         int c = a + b;
>     doesn't affect any object field initialization.
>     It's just a local variable, which gets lost after the instance is instantiated.
>
>     As workaround, you can always use a static helper method which does the same:
>         super(staticHelper(a, b));
>
>     So I agree, it would reasonable, to allow some code in advance of this() or super().
>