Name: bsC130419 Date: 08/02/2001


java version "1.4.0-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-beta-b65)
Java HotSpot(TM) Client VM (build 1.4.0-beta-b65, mixed mode)

The specification for java.lang.reflect.Proxy.newProxyInstance requires a
NullPointerException if the InvocationHandler argument is null. However, this
same restriction does not currently apply to proxy instances constructed by
reflection. I propose that the Proxy constructor be modified to throw a
NullPointerException if parameter h is null and isProxyInstance() returns true,
so that it is impossible to create a proxy instance without a handler, rather
than the current problem of failing at an undetermined point later on when the
handler is first used.

This class shows the difference:
import java.lang.reflect.*;
class Foo {
  public static void main(String[] args) {
    Object o = null;
    try {
      o = Proxy.newProxyInstance(Foo.class.getClassLoader(),
                                 new Class[0], null);
    } catch (NullPointerException e) {
      System.out.println("newProxyInstance OK");
    }
    try {
      o = Proxy.getProxyClass(Foo.class.getClassLoader(),
                              new Class[0]).
            getConstructor(new Class[] {InvocationHandler.class}).
            newInstance(new Object[1]);
      System.out.println("Oops, created proxy instance without handler");
    } catch (NullPointerException e) {
      System.out.println("Proxy constructor OK");
    } catch (Exception e) {
      System.out.println("shouldn't get here");
    }
    if (o != null)
      try {
        System.out.println(o);
      } catch (NullPointerException e) {
        System.out.println("Delayed failure is BAD");
        e.printStackTrace();
      }
  }
}

Implementation wise, all you need do is change Proxy(InvocationHandler h),
adding a check:
if (h == null && isProxyInstance(this)) throw new NullPointerException();
(Review ID: 129305)
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