Pattern, Abstract Factory / Factory

[Rudi Araújo]

Class::newInstance() doesn't have any parameters (also, it's deprecated:
better to use getConstructor() or getDeclaredConstructor() and call
newInstance() on it).

Also, the generic agreement on your calls to makeAndPrint is failing.

This does what you wanted:

jshell> class Foo { }
|  modified class Foo

jshell> class Bar extends Foo { }
|  modified class Bar

jshell> class Baz extends Foo { }
|  modified class Baz

jshell> class Main {
   ...>   public static void main(String[] args) {
   ...>     makeAndPrint(Foo.class);
   ...>     makeAndPrint(Bar.class);
   ...>     makeAndPrint(Baz.class);
   ...>   }
   ...>
   ...>   public static void makeAndPrint(Class<? extends Foo> klass) {
   ...>     try {
   ...>       Object o = klass.newInstance();
   ...>       System.out.println("Created: " + o.toString());
   ...>     } catch (Exception e) {
   ...>       System.err.println("Failed: " + klass);
   ...>     }
   ...>   }
   ...> }
|  created class Main

jshell> Main.main(new String[]{})
Created: REPL.$JShell$11$Foo at 6a4f787b
Created: REPL.$JShell$12$Bar at 7d9d1a19
Created: REPL.$JShell$13$Baz at 39c0f4a


On Sat, 6 Feb 2021 at 20:56, Luís Oliveira <luismbo at gmail.com> wrote:

> On Sat, 6 Feb 2021 at 16:29, Manfred Bergmann <manfred.bergmann at me.com>
> wrote:
> > But this is kind of also possible in i.e. Java where you can say:
> > Foo.class.newInstance() which uses reflection and is not normally used.
> > But is effectively similar to make-instance `foo.
>
>  My Java is getting rustier and rustier, but maybe you can tell me why
> the following program doesn't compile:
>
> class Foo { }
> class Bar extends Foo { }
> class Baz extends Foo { }
>
> class Main {
>   public static void main(String[] args) {
>     makeAndPrint(Foo.class);
>     makeAndPrint(Bar.class);
>     makeAndPrint(Baz.class);
>   }
>
>   public static void makeAndPrint(Class<Foo> klass) {
>     try {
>       Object o = klass.newInstance(klass);
>       System.out.println("Created: " + o.toString());
>     } catch (Exception e) {
>       System.err.println("Failed: " + klass);
>     }
>   }
> }
>
> The rough equivalent in Common Lisp would be:
>
> (defclass foo () ())
> (defclass bar (foo) ())
> (defclass baz (foo) ())
>
> (mapcar #'make-instance '(foo bar baz))
>
> Luís
>
>

-- 
He who binds to himself a joy
Doth the winged life destroy
But he who kisses the joy as it flies
Lives in Eternitys sun rise

- William Blake
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