I was going over the flume 1.2.0 code and i was wondering why
the ComponentConfigurationFactory.create class has the following:

confType = (Class<? extends ComponentConfiguration>) Class.forName(type);
return confType.getConstructor(String.class).newInstance(type);

Since type is the class, then why does the the class need a constructor
that puts in the class name?

thanks for your time reading this email.

From: http://docs.oracle.com/javase/tutorial/reflect/member/ctorInstance.html
There are two reflective methods for creating instances of classes: java.lang.reflect.Constructor.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29) and Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29). The former is preferred and is thus used in these examples because:
Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29) can only invoke the zero-argument constructor, while Constructor.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29) may invoke any constructor, regardless of the number of parameters.
Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29) throws any exception thrown by the constructor, regardless of whether it is checked or unchecked. InvocationTargetException (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/InvocationTargetException.html).
Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29) requires that the constructor be visible; Constructor.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29) may invoke private constructors under certain circumstances.
Thanks,
Hari

--
Hari Shreedharan
On Wednesday, September 19, 2012 at 10:20 PM, David Capwell wrote:

> I was going over the flume 1.2.0 code and i was wondering why
> the ComponentConfigurationFactory.create class has the following:
>
> confType = (Class<? extends ComponentConfiguration>) Class.forName(type);
> return confType.getConstructor(String.class).newInstance(type);
>
> Since type is the class, then why does the the class need a constructor
> that puts in the class name?
>
> thanks for your time reading this email.

I guess my real question would be why my custom ComponentConfiguration has
to have this constructor.  Here is quick sample of what i mean:

public void createInstance() {
    final ComponentConfiguration config ComponentConfigurationFactory.create(
        "name",
        RandomConfig.class.getName(),
        ComponentConfiguration.ComponentType.SOURCE);
  }

  public static class RandomConfig extends ComponentConfiguration {

    public RandomConfig() {
      super("my awesome name");
    }
  }

This fails since the constructor doesn't exist.  If i add a param "String
ignored" then it works just fine.

On Wed, Sep 19, 2012 at 10:47 PM, Hari Shreedharan <
[EMAIL PROTECTED]> wrote:

>  From:
> http://docs.oracle.com/javase/tutorial/reflect/member/ctorInstance.html
>
> *There are two reflective methods for creating instances of classes:
> java.lang.reflect.Constructor.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29>and
> Class.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29>.
> The former is preferred and is thus used in these examples because:*
>
>    - *Class.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29>can only invoke the zero-argument constructor, while
>    Constructor.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29>may invoke any constructor, regardless of the number of parameters.
>    *
>    - *Class.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29>throws any exception thrown by the constructor, regardless of whether it is
>    checked or unchecked. InvocationTargetException<http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/InvocationTargetException.html>
>    .*
>    - *Class.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29>requires that the constructor be visible;
>    Constructor.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29>may invoke
>    private constructors under certain circumstances.*
>
>
>
> Thanks,
> Hari
>
> --
> Hari Shreedharan
>
> On Wednesday, September 19, 2012 at 10:20 PM, David Capwell wrote:
>
> I was going over the flume 1.2.0 code and i was wondering why
> the ComponentConfigurationFactory.create class has the following:
>
> confType = (Class<? extends ComponentConfiguration>) Class.forName(type);
> return confType.getConstructor(String.class).newInstance(type);
>
> Since type is the class, then why does the the class need a constructor
> that puts in the class name?
>
> thanks for your time reading this email.
>
>
>

I don't remember why I did this at that time. I will take a look at this when I get some time and get back to you. FWIW, this is part of a yet to be completed component-wise configuration system which I plan to get back to some time soon. Hopefully, this is not a blocker for you as of now.  

Thanks,
Hari

--
Hari Shreedharan
On Wednesday, September 19, 2012 at 11:02 PM, David Capwell wrote:

> I guess my real question would be why my custom ComponentConfiguration has to have this constructor.  Here is quick sample of what i mean:
>
> public void createInstance() {
>     final ComponentConfiguration config = ComponentConfigurationFactory.create(
>         "name",
>         RandomConfig.class.getName(),
>         ComponentConfiguration.ComponentType.SOURCE);
>   }
>
>   public static class RandomConfig extends ComponentConfiguration {
>
>     public RandomConfig() {
>       super("my awesome name");
>     }
>   }
>
>
> This fails since the constructor doesn't exist.  If i add a param "String ignored" then it works just fine.
> On Wed, Sep 19, 2012 at 10:47 PM, Hari Shreedharan <[EMAIL PROTECTED] (mailto:[EMAIL PROTECTED])> wrote:
> > From: http://docs.oracle.com/javase/tutorial/reflect/member/ctorInstance.html
> > There are two reflective methods for creating instances of classes: java.lang.reflect.Constructor.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29) and Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29). The former is preferred and is thus used in these examples because:
> > Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29) can only invoke the zero-argument constructor, while Constructor.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29) may invoke any constructor, regardless of the number of parameters.
> > Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29) throws any exception thrown by the constructor, regardless of whether it is checked or unchecked. InvocationTargetException (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/InvocationTargetException.html).
> > Class.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29) requires that the constructor be visible; Constructor.newInstance() (http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29) may invoke private constructors under certain circumstances.
> >
> >
> >
> >
> > Thanks,
> > Hari
> >
> > --
> > Hari Shreedharan
> >
> >
> > On Wednesday, September 19, 2012 at 10:20 PM, David Capwell wrote:
> >
> > > I was going over the flume 1.2.0 code and i was wondering why
> > > the ComponentConfigurationFactory.create class has the following:
> > >
> > > confType = (Class<? extends ComponentConfiguration>) Class.forName(type);
> > > return confType.getConstructor(String.class).newInstance(type);
> > >
> > > Since type is the class, then why does the the class need a constructor
> > > that puts in the class name?
> > >
> > > thanks for your time reading this email.
> >
>

Its not a blocker.  I have a setup working right now for what we are trying
to do.

On Thu, Sep 20, 2012 at 11:56 AM, Hari Shreedharan <
[EMAIL PROTECTED]> wrote:

>  I don't remember why I did this at that time. I will take a look at this
> when I get some time and get back to you. FWIW, this is part of a yet to be
> completed component-wise configuration system which I plan to get back to
> some time soon. Hopefully, this is not a blocker for you as of now.
>
> Thanks,
> Hari
>
> --
> Hari Shreedharan
>
> On Wednesday, September 19, 2012 at 11:02 PM, David Capwell wrote:
>
> I guess my real question would be why my custom ComponentConfiguration has
> to have this constructor.  Here is quick sample of what i mean:
>
> public void createInstance() {
>     final ComponentConfiguration config > ComponentConfigurationFactory.create(
>         "name",
>         RandomConfig.class.getName(),
>         ComponentConfiguration.ComponentType.SOURCE);
>   }
>
>   public static class RandomConfig extends ComponentConfiguration {
>
>     public RandomConfig() {
>       super("my awesome name");
>     }
>   }
>
> This fails since the constructor doesn't exist.  If i add a param "String
> ignored" then it works just fine.
>
> On Wed, Sep 19, 2012 at 10:47 PM, Hari Shreedharan <
> [EMAIL PROTECTED]> wrote:
>
>  From:
> http://docs.oracle.com/javase/tutorial/reflect/member/ctorInstance.html
>
> *There are two reflective methods for creating instances of classes:
> java.lang.reflect.Constructor.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29>and
> Class.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29>.
> The former is preferred and is thus used in these examples because:*
>
>    - *Class.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29>can only invoke the zero-argument constructor, while
>    Constructor.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29>may invoke any constructor, regardless of the number of parameters.
>    *
>    - *Class.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29>throws any exception thrown by the constructor, regardless of whether it is
>    checked or unchecked. InvocationTargetException<http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/InvocationTargetException.html>
>    .*
>    - *Class.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29>requires that the constructor be visible;
>    Constructor.newInstance()<http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Constructor.html#newInstance%28java.lang.Object...%29>may invoke
>    private constructors under certain circumstances.*
>
>
>
> Thanks,
> Hari
>
> --
> Hari Shreedharan
>
> On Wednesday, September 19, 2012 at 10:20 PM, David Capwell wrote:
>
> I was going over the flume 1.2.0 code and i was wondering why
> the ComponentConfigurationFactory.create class has the following:
>
> confType = (Class<? extends ComponentConfiguration>) Class.forName(type);
> return confType.getConstructor(String.class).newInstance(type);
>
> Since type is the class, then why does the the class need a constructor
> that puts in the class name?
>
> thanks for your time reading this email.
>
>
>
>
>