Name: pa48320 Date: 07/12/2002

Create an abstract class that depends on subclasses. When you load a subclass using Class.forName(), you will get a ClassLinkageError. This is new in 1.4 (I only tried 1.4.1) and does not happen in 1.3.1_03.
Create the following class:
public class Main
{
    public static void main(String [] args) {
        try {
            Class cl = Class.forName("pkg.Item1");
        } catch (Throwable t) {
            t.printStackTrace();
        }
        System.out.println("Done.");
    }
}

Create the following 3 classes and put them in a jar file and put that jar file in the extensions directory:
package pkg;
public abstract class Item
{
    public Item getItem(int type) {
        if (type == 1) {
            return new Item1();
        } else if (type == 2) {
            return new Item2();
        } else {
            return null;
        }
    }

    public abstract String myName();
}
package pkg;
public class Item1 extends Item
{
    public String myName() {
        return "Item 1";
    }
}
package pkg;
public class Item2 extends Item
{
    public String myName() {
        return "Item 2";
    }
}


Now execute the first class. If you execute -verbose:class you will see output like this:
<whole bunch of class loads deleted>
[Loaded pkg.Item]
[Loaded pkg.Item1]
[Loaded pkg.Item2]
[Loaded pkg.Item1]
[Loaded java.lang.ClassFormatError from C:\j2sdk1.4.1\jre\lib\rt.jar]
java.lang.LinkageError: duplicate class definition: pkg/Item1
[Loaded java.lang.StackTraceElement from C:\j2sdk1.4.1\jre\lib\rt.jar]
at java.lang.ClassLoader.defineClass0(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:502)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:123)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:250)
at java.net.URLClassLoader.access$100(URLClassLoader.java:54)
at java.net.URLClassLoader$1.run(URLClassLoader.java:193)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:186)
at java.lang.ClassLoader.loadClass(ClassLoader.java:299)
at java.lang.ClassLoader.loadClass(ClassLoader.java:292)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:265)
at java.lang.ClassLoader.loadClass(ClassLoader.java:255)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:315)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:140)
at Main.main(Main.java:5)
Done.

If you execute this in 1.3.1 you will see the following output:
<whole bunch of class loads deleted>
[Loaded pkg.Item]
[Loaded pkg.Item1]
[Loaded pkg.Item2]
Done.
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