why ClassCastException ?

[siv sanny]

See this code, I think its simple to understand;
Here are my questions
1. since there are two instances of Same Class, which will be considered when i refered that class(creating a new instance or acceing a member)?
2. How can i access data in the second case ?

public class SMT {
    public static int data = 1234;
    public static void main(String[] args)
    {
        // code to set SecurityManager
 
        System.out.println("data  ===>" + data );
        data = 9999999;
        URL[] url = {new URL("file://D:/Myworkspace/")};//url of SMT Class
        Class c = new URLClassLoader(url, null).loadClass("SMT");//reload
        System.out.println(c.getClassLoader());
        Object o = c.newInstance();
        System.out.println(((SMT)o).data );                   
    }
}

O/p
data ===> 1234
java.net.URLClassLoader@422ede
java.lang.ClassCastException
at SMT.main(SMT.java:39)


thanks
-ssv
[ August 10, 2005: Message edited by: sankar vas ]

[Joshua Bloch]

Sankar,

The problem is that you have two different, unrelated classes, both named SMT. One is the class whose source code you've provided and the other one is the one that you load explicitly with this line:

        Class c = new URLClassLoader(url, null).loadClass("SMT");//reload

The name of a class consists of three parts: the simple (unqualified) name, the package name, and the class loader. In this case, you have two classes with the same simple name and package names, but different class loader names. They are unlrelated. The comment "//reload" is wrong. The original class is still there.

A wise man once said "When the code and the comment disagree, both are probably wrong "

Regards,

Josh

[Norm Radder]

I don't get the same error? Probably Classpath?

import java.util.*;
import java.net.*;

public class SMT {
public static int data = 1234;
public static void main(String[] args) throws Exception
{
// code to set SecurityManager
System.out.println("data ===>" + data );
data = 9999999;
URL[] url = {new URL("file://D:/Myworkspace/")};//url of SMT Class
Class c = new URLClassLoader(url, null).loadClass("SMT");//reload
System.out.println(c.getClassLoader());
Object o = c.newInstance();
System.out.println(((SMT)o).data );

}
}/* Output when executed:
Running: java SMT

data ===>1234
java.lang.ClassNotFoundException: SMT
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at SMT.main(SMT.java)
Exception in thread "main"
0 error(s)
*/

[Ernest Friedman-Hill]

Originally posted by Norm Radder:
URL[] url = {new URL("file://D:/Myworkspace/")};//url of SMT Class

Unless your copy of SMT.class is in this same directory, then yes. This has to be changed to match your setup.

[siv sanny]

        Class c = new URLClassLoader(url, null).loadClass("SMT");//reload

The name of a class consists of three parts: the simple (unqualified) name, the package name, and the class loader. In this case, you have two classes with the same simple name and package names, but different class loader names. They are unlrelated. The comment "//reload" is wrong. The original class is still there.

A wise man once said "When the code and the comment disagree, both are probably wrong "

Regards,

Josh[/qb]<hr></blockquote>


thanks very much for your comments. however, i am still not clear.

let me put my question clearly : here i have two class loaders, one system class loader and one my own loader, loading one class SMT twice, so when i try to cast the object returned by my class loader it gives me a exception ...so how am i supposed to cast it ???... do i say ((myclassLoader.SMT)o).data ??? or something like that ??? how do i identify a class with those 3 things classloader.packageName.className ???

point to note : i have given 'null' as parent class loader to my class loader.
[ August 11, 2005: Message edited by: sankar vas ]