How do I pass parameter when using newInstance

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Tony Johansson - 19 Oct 2005 12:37 GMT

Hello!

I use method forName and newInstance in class Class like this
instance = (GameFactory)(Class.forName(name).newInstance() );

Now to my question:
Assume that name is GameFactory then I want to pass a parameter to the
GameFactory constructor
like this instance = (GameFactory)(Class.forName(name).newInstance(field) );
Here I pass parameter field which is an int but when I do so I get compile
error saying

F:\gameLab\GameFactory.java(15): Cannot find method 'newInstance(int)' in
'java.lang.Class'

How you any idea?

Or is it so that if I want to pass parameter I have to explicitly use new
GameFactory(field);

//Tony

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Oliver Wong - 19 Oct 2005 16:06 GMT

> Hello!
>
[quoted text clipped - 16 lines]
> Or is it so that if I want to pass parameter I have to explicitly use new
> GameFactory(field);

In short, you can't do this. From the JavaDocs:

<quote>
Creates a new instance of the class represented by this Class object. The
class is instantiated as if by a new expression with an empty argument list.
</quote>

- Oliver

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Ian Shef - 19 Oct 2005 19:50 GMT

> Hello!
>
[quoted text clipped - 11 lines]
> F:\gameLab\GameFactory.java(15): Cannot find method 'newInstance(int)'
> in 'java.lang.Class'

<snip>

I don't think that you can do this with Class, but you can use the reflection
package java.lang.reflect . Use Class.getConstructor or
Class.getConstructors to get an appropriate Constructor. Then use
Constructor.newInstance to create and initialize an instance.

It is going to be more complex than the no-argument constructor that you were
using before.

Good Luck!

Signature

Ian Shef 805/F6 * These are my personal opinions
Raytheon Company * and not those of my employer.
PO Box 11337 *
Tucson, AZ 85734-1337 *

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How do I pass parameter when using newInstance

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