A problem about proxies

[ZelluX]

I'm reading the chapter about proxies on Core Java 2
The book give a TraceHandler class as an example, which will print the
name of the method to be called.

import java.lang.reflect.*;

public class TraceHandler implements InvocationHandler {
private Object target;

public TraceHandler(Object t) {
target = t;
}

public Object invoke(Object proxy, Method m, Object[] args) throws
Throwable {
System.out.println("Method " + m + "invoked.");
return m.invoke(target, args);
}
}

I wrote a test interface and a class whichi implements it:
public interface MyInterface {
int factorial(int n);
void empty();
void printSomething();
}

public class TargetObject implements MyInterface {
public int factorial(int n) {
return n <= 1 ? 0 : n * factorial(n - 1);
}

public void empty() {
}

public void printSomething() {
System.out.println("Hello world as always");
}
}

and a test class
import java.lang.reflect.*;

public class Test {
public static void main(String[] args) {
Object target = new TargetObject();
InvocationHandler handler = new TraceHandler(target);
Class[] interfaces = target.getClass().getInterfaces();
Object proxy = Proxy.newProxyInstance(null, interfaces,
handler);
}
}

But when i ran this Test program, it throws an exception
Exception in thread "main" java.lang.IllegalArgumentException:
interface MyInterface is not visible from class loader
at java.lang.reflect.Proxy.getProxyClass(Proxy.java:353)
at java.lang.reflect.Proxy.newProxyInstance(Proxy.java:581)
at Test.main(Test.java:9)

How to deal with this problem?

many thanks

 

[ZelluX]

You specified null as the class loader. Perhaps try
ClassLoader.getSystemClassLoader()?

It works!
But on the book it says `For now, we specify null to use the default
class loader.'. In this program null doesn't mean to use default class
loader?

 

[Roedy Green]

How to deal with this problem?

I would try putting everything into an explicit package.

 

[Roedy Green]

It works!
But on the book it says `For now, we specify null to use the default
class loader.'. In this program null doesn't mean to use default class
loader?

there is no mention of the null convention at
http://java.sun.com/javase/6/docs/api/java/lang/reflect/Proxy.html

Presumably Marty discovered this undocumented behaviour, and Sun later
changed it.