InstantiationException - Java library calling newInstance method on Scala class

[RanUser]

I'm greatful for any direction on this one!

- Scala 2.9.2

I'm using the Cassandra Astyanax client library, which is throwing an
InstantiationException here:

private T createContents(Class<T> clazz) throws
InstantiationException, IllegalAccessException {
return clazz.newInstance();
}

The relevant exception portion:

...
at java.lang.reflect.Method.invoke(Method.java:601)
Caused by: java.lang.InstantiationException: com.ranuser.TestClient
$TestCompositeColumn
at java.lang.Class.newInstance0(Class.java:357)
at java.lang.Class.newInstance(Class.java:325)
at
com.netflix.astyanax.serializers.AnnotatedCompositeSerializer.createContents(AnnotatedCompositeSerializer.java:
167)

--

Astyanax requires a class with a zero arg constructor, and possibly a
multi argument class constructor (from what I've read):

class TestCompositeColumn(idIn: Long, key1In: String, key2In: String)
extends Ordered[TestCompositeColumn] {
@Component(ordinal = 0) var id: Long = idIn
@Component(ordinal = 1) var key1: String = key1In
@Component(ordinal = 2) var key2: String = key2In

def this() = this(0, null, null)
//equals, hashCode, compare all implemented
}

I also defined an companion object to try to simulate Java static
newInstance method (newInstance method is never reached, and I'm sure
I'm doing it wrong):

object TestCompositeColumn{
def newInstance() = new TestCompositeColumn
}

[Alex Cruise]

On Wed, Sep 12, 2012 at 9:15 PM, RanUser <ranu...@gmail.com> wrote:
> Astyanax requires a class with a zero arg constructor, and possibly a
> multi argument class constructor (from what I've read):
>
> class TestCompositeColumn(idIn: Long, key1In: String, key2In: String)
> extends Ordered[TestCompositeColumn] {
> @Component(ordinal = 0) var id: Long = idIn
> @Component(ordinal = 1) var key1: String = key1In
> @Component(ordinal = 2) var key2: String = key2In
>
> def this() = this(0, null, null)
> //equals, hashCode, compare all implemented
> }

It may help to add the @field meta-annotation to make sure the
annotations get applied to the fields, instead of (or in addition to?)
the getters. The syntax is a bit ugly, but this is how you do it:

import annotation.target.field

class Foo {
@(AnnotationWithoutParams @field)
@(AnnotationWithParams @field)(param=value)
guid: String

}

> I also defined an companion object to try to simulate Java static
> newInstance method (newInstance method is never reached, and I'm sure
> I'm doing it wrong):

This doesn't work in Java; newInstance is a non-static method of a
Class, not a static method of a class. :)

-0xe1a

[RanUser]

I tried the annotation tip but still have the same exception.  I believe annotations are working because I can insert into the DB.

 

The problem continues to be the call to clazz.newInstance() . I also tried defining def newInstance() = new TestCompositeColumn() in the TestCompositeColumn class unsuccessfully as well.

 

Any other ideas how to deal with this clazz.newInstance() call made from the java library to my class?

 

Thanks!

[Alex Cruise]

On Thu, Sep 13, 2012 at 1:47 PM, RanUser <ranu...@gmail.com> wrote:
> I tried the annotation tip but still have the same exception.  I believe
> annotations are working because I can insert into the DB.

Oh OK!  

Caused by: java.lang.InstantiationException: com.ranuser.TestClient$TestCompositeColumn

This is a clue though!  Inner classes in Scala have a hidden constructor parameter that's probably not being supplied here.  Try moving TestCompositeColumn to the top-level.  It doesn't have to be in its own file, just make it a peer of TestClient instead of a child.

> The problem continues to be the call to clazz.newInstance() . I also tried
> defining def newInstance() = new TestCompositeColumn() in the
> TestCompositeColumn class unsuccessfully as well.

Yeah, you're not going to get anywhere trying to override/define/redefine newInstance.  This document, and the surrounding Java reflection tutorial, will hopefully shed some light. :)

http://docs.oracle.com/javase/tutorial/reflect/member/ctorTrouble.html

-0xe1a

[RanUser]

Another set of eyes does wonders :)

 

The exception was due to TestCompositeColumn being an inner class as you suggested.

 

Thanks so much!