Instantiating a Class

[Vijay Singh]

How do you instantiat a class with a Class.forName( ) method, if the class's
default constructor requires a parameter?

[D Goldman]

"Vijay Singh" <vi*******@hotmail.com> wrote in message news:<ef****************@news-binary.blueyonder.co.uk>...

How do you instantiat a class with a Class.forName( ) method, if the class's
default constructor requires a parameter?

The Class.forName(...) method only loads the class and executes any
static initializers there may be. It does not instantiate any objects
of the class (except if a static initializer does that). If you write
Class.forName("X").newInstance(), however, that will create a new
instance of the class, using the constructor with zero parameters.

You can do the following

You can only use the default constructor however (the one with
no parameters), if you wish to pass in parameters you must
create an init() method (or similar) for the class being created
and then you can call it as:

Class class = Class.forName("MyClass");
Object object = class.newInstance();
MyClass myClass = (MyClass) object;
myClass.init(int myParameter, MyOtherClasses myParameter2);

Hope this helps,
Daniel Goldman
http://d-goldman.org

[Soren]

D Goldman wrote:

"Vijay Singh" <vi*******@hotmail.com> wrote in message news:<ef****************@news-binary.blueyonder.co.uk>...

How do you instantiat a class with a Class.forName( ) method, if the class's
default constructor requires a parameter?

The Class.forName(...) method only loads the class and executes any
static initializers there may be. It does not instantiate any objects
of the class (except if a static initializer does that). If you write
Class.forName("X").newInstance(), however, that will create a new
instance of the class, using the constructor with zero parameters.

You can do the following

You can only use the default constructor however (the one with
no parameters), if you wish to pass in parameters you must
create an init() method (or similar) for the class being created
and then you can call it as:

Class class = Class.forName("MyClass");
Object object = class.newInstance();
MyClass myClass = (MyClass) object;
myClass.init(int myParameter, MyOtherClasses myParameter2);

Hope this helps,
Daniel Goldman
http://d-goldman.org

If your class Foo has a constructor like, say

Foo (int i, String s) {...}
You might use
Class cfoo = Class.forName("Foo");
Constructor con = cfoo.getConstructor(Integer.TYPE, String.class);
Object o = con.newInstance(new Object[]{new Integer(27), "Hi !"});
Foo foo = (Foo)o;

add appropriate exception handling :)

Soren