Class loading and Java Generic

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Ian - 27 Jan 2006 19:18 GMT

I am new to java class loading. In using it, I have two questions based
on the following code:

Class cc = Class.forName("G2");
G2 g = (G2)cc.newInstance();

1. When calling newInstance() to initialize "g", should G2 have to have
a default constructor without any parameters (i.e. public G2() {...}) ?
If yes, is there anyway to get around this if every G2's constructor
has at least one parameter? If no, how to call newInstance() in a
proper way?

2. What if G2 is a Java Generic class, e.g., G2<String, Int>? I tried
it. Except some "parameterize" warning messages at compile time, it
works fine. But my question is, is it safe?

Thanks.

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oulan bator - 27 Jan 2006 19:35 GMT

hi,

1- yes of course, but you can get through this, using the
getConstructor() see
(http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Class.html#getDeclaredConstruc
tor(java.lang.Class...))

2- I don't know, but I would like to kown

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Thomas Hawtin - 27 Jan 2006 19:35 GMT

> Class cc = Class.forName("G2");
> G2 g = (G2)cc.newInstance();
[quoted text clipped - 4 lines]
> has at least one parameter? If no, how to call newInstance() in a
> proper way?

Get a Constructor from the Class and call newInstance on that.
Class.newInstance should be avoided anyway because of its eccentric
exception behaviour.

> 2. What if G2 is a Java Generic class, e.g., G2<String, Int>? I tried
> it. Except some "parameterize" warning messages at compile time, it
> works fine. But my question is, is it safe?

It's a good idea to avoid using generic types in this sort of situation.
Kind of difficult with serialisation, but such is life.

Tom Hawtin

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Unemployed English Java programmer
http://jroller.com/page/tackline/

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Class loading and Java Generic

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