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Java Forum / General / July 2007

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reflection problem

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xareon@gmail.com - 25 Jul 2007 15:33 GMT
hi all, i got a problem with this bunch of code:

[CODE]
Manager boss = new Manager("Paul Brown", 1000, 500);

Class c = boss.getClass();

try
{
Field field = c.getField("bonus");

Integer newBonus = field.getInt(boss);
newBonus = newBonus + 200;
field.setInt(boss, newBonus);

}
catch(NoSuchFieldException nsfe)
{
System.out.println(nsfe.getMessage());
nsfe.printStackTrace();
}
catch(IllegalAccessException iae)
{
System.out.println(iae.getMessage());
iae.printStackTrace();
}
[/CODE]

i got a class Manager with a public (otherwise i'd get a
NoSuchFieldException) Integer bonus field. i'd like to modify it via
reflection, but i get an error at this point:

Integer newBonus = field.getInt(boss);

[CODE]Exception in thread "main" java.lang.IllegalArgumentException:
Attempt to get java.lang.Integer field "dynamicbinding.Manager.bonus"
with illegal data type conversion to int
at
sun.reflect.UnsafeFieldAccessorImpl.newGetIllegalArgumentException(Unknown
Source)
at
sun.reflect.UnsafeFieldAccessorImpl.newGetIntIllegalArgumentException(Unknown
Source)
at sun.reflect.UnsafeObjectFieldAccessorImpl.getInt(Unknown Source)
at java.lang.reflect.Field.getInt(Unknown Source)
at reflection.Main.main(Main.java:30)[/CODE]

illegal data type conversion to int? what does it mean? how can i fix
this? thank you all :)
Daniel Pitts - 25 Jul 2007 15:44 GMT
On Jul 25, 7:33 am, xar...@gmail.com wrote:
> hi all, i got a problem with this bunch of code:
>
[quoted text clipped - 46 lines]
> illegal data type conversion to int? what does it mean? how can i fix
> this? thank you all :)

getInt returns (int), where as your Bonus value is an Integer.

You can either change the type of your bonus to int, or you can use
Integer newBonus = (Integer)field.get(boss);

Although, I'm curious why you wish to use Reflection.  If your project
is simply to learn more about reflection, thats fine, but usually
using reflection for this sort of thing is a Bad Idea (TM).  Perhaps
if you shared your goal with the group, we could suggest a better way.
xareon@gmail.com - 25 Jul 2007 15:59 GMT
> On Jul 25, 7:33 am, xar...@gmail.com wrote:
>
[quoted text clipped - 58 lines]
> using reflection for this sort of thing is a Bad Idea (TM).  Perhaps
> if you shared your goal with the group, we could suggest a better way.

thank you man. although it sounds me funky to get an error with the
int/Integer assignaments (wrapper classes shouldn't give such
problems), i've tried your solution, and this one too:

int newBonus = f.getInt(boss);

but i keep on getting the same error at the same line. and finally
yes, my project is simply to learn more about reflection. i know i
could have simply done this via standard set/get methods :)
plus, to allow a pure OO programming, i'd avoid to change the type of
bonus from Integer to int :)
xareon@gmail.com - 25 Jul 2007 16:09 GMT
On 25 Lug, 16:59, xar...@gmail.com wrote:

> > On Jul 25, 7:33 am, xar...@gmail.com wrote:
>
[quoted text clipped - 70 lines]
> plus, to allow a pure OO programming, i'd avoid to change the type of
> bonus from Integer to int :)

ty, i found the problem: it was just that getInt() method returns an
int, while my field was an Integer. i should have used

Integer newBonus = (Integer)f.get(boss);

get returns an object, that i just cast to Integer. sometimes i feel
so stupid :x
xareon@gmail.com - 25 Jul 2007 16:14 GMT
On 25 Lug, 16:59, xar...@gmail.com wrote:

> > On Jul 25, 7:33 am, xar...@gmail.com wrote:
>
[quoted text clipped - 70 lines]
> plus, to allow a pure OO programming, i'd avoid to change the type of
> bonus from Integer to int :)

ty, i found the problem: it was just that getInt() method returns an
int, while my field was an Integer. i should have used

Integer newBonus = (Integer)f.get(boss);

get returns an object, that i just cast to Integer. sometimes i feel
so stupid :x
xareon@gmail.com - 25 Jul 2007 16:18 GMT
On 25 Lug, 16:59, xar...@gmail.com wrote:

> > On Jul 25, 7:33 am, xar...@gmail.com wrote:
>
[quoted text clipped - 70 lines]
> plus, to allow a pure OO programming, i'd avoid to change the type of
> bonus from Integer to int :)

ty, i found the problem: it was just that getInt() method returns an
int, while my field was an Integer. i should have used

Integer newBonus = (Integer)f.get(boss);

get returns an object, that i just cast to Integer. sometimes i feel
so stupid :x
xareon@gmail.com - 25 Jul 2007 16:08 GMT
> On Jul 25, 7:33 am, xar...@gmail.com wrote:
>
[quoted text clipped - 58 lines]
> using reflection for this sort of thing is a Bad Idea (TM).  Perhaps
> if you shared your goal with the group, we could suggest a better way.

thank you man. although it sounds me funky to get an error with the
int/Integer assignaments (wrapper classes shouldn't give such
problems), i've tried your solution, and this one too:

int newBonus = f.getInt(boss);

but i keep on getting the same error at the same line. and finally
yes, my project is simply to learn more about reflection. i know i
could have simply done this via standard set/get methods :)
plus, to allow a pure OO programming, i'd avoid to change the type of
bonus from Integer to int :)


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