Confirm bug in java.lang.reflect.Proxy wrt static methods in interfaces

[mandy chung]

FYI. I created https://bugs.openjdk.java.net/browse/JDK-8188240 for this 
issue.

Mandy

On 10/2/17 1:33 PM, mandy chung wrote:
> I believe it is a bug.   To invoke a static method in the proxy 
> interface, it will have to do "I1.foo()" or "I2.foo()".  It won't 
> invoke through the proxy object, i.e. it's not interceptible. Even 
> creating a proxy for I1, the generated proxy class includes an 
> instance method named "foo" and no static method is generated in the 
> proxy class.
>
> Mandy
>
> On 10/2/17 11:44 AM, Eric McCorkle wrote:
>> Hello everyone,
>>
>> A colleague of mine discovered what seems to be a bug in
>> java.lang.reflect.Proxy#newProxyInstance.  I'd like to confirm that this
>> is indeed incorrect behavior before I go and fix it.
>>
>> Consider the following two interfaces:
>>
>> interface I1 {
>>    static I1 foo() {
>>      return null;
>>    }
>> }
>>
>> interface I2 {
>>    static I2 foo() {
>>      return null;
>>    }
>> }
>>
>> JLS 9.4.1 states that static methods are not inherited in interfaces,
>> thus it should be perfectly legal to define some class which inherits I1
>> and I2.
>>
>> The following proxy creation fails:
>>
>> public class ProxyBug {
>>    public static void main(String... args) {
>>      I2 i2 =(I2)Proxy.newProxyInstance(
>>                   ClassLoader.getSystemClassLoader(),
>>                   new Class[] {I1.class, I2.class},
>>                   new InvocationHandler() {
>>                     @Override
>>                     public Object invoke(Object proxy,
>>                                          Method method,
>>                                          Object[] args)
>>                       throws Throwable {
>>                       return null;
>>                     }
>>                   });
>>    }
>> }
>>
>> The exception generated is as follows:
>>
>> Exception in thread "main" java.lang.IllegalArgumentException: methods
>> with same signature foo() but incompatible return types: [interface I1,
>> interface I2]
>>     at sun.misc.ProxyGenerator.checkReturnTypes(ProxyGenerator.java:712)
>>     at 
>> sun.misc.ProxyGenerator.generateClassFile(ProxyGenerator.java:461)
>>     at 
>> sun.misc.ProxyGenerator.generateProxyClass(ProxyGenerator.java:339)
>>     at java.lang.reflect.Proxy$ProxyClassFactory.apply(Proxy.java:639)
>>     at java.lang.reflect.Proxy$ProxyClassFactory.apply(Proxy.java:557)
>>     at java.lang.reflect.WeakCache$Factory.get(WeakCache.java:230)
>>     at java.lang.reflect.WeakCache.get(WeakCache.java:127)
>>     at java.lang.reflect.Proxy.getProxyClass0(Proxy.java:419)
>>     at java.lang.reflect.Proxy.newProxyInstance(Proxy.java:719)
>>     at ProxyBug.main(ProxyBug.java:19)
>>
>> So it would seem that newProxyInstance is incorrectly including static
>> methods in its check for incompatible return types.
>>
>> Can I get someone from core-libs to confirm that this is not intended
>> before I file a bug and start on the fix?
>