FULL PRODUCT VERSION :
java version "1.8.0_92"
Java(TM) SE Runtime Environment (build 1.8.0_92-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.92-b14, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Linux Mint 17.1 - 64 bit, uname -a output is:

Linux 3.13.0-37-generic #64-Ubuntu SMP Mon Sep 22 21:28:38 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux


A DESCRIPTION OF THE PROBLEM :
I have a pretty straightforward code which does a lookup of a method using reflection and then invokes on it, passing it some params. If the wrong number of method params are passed it is expected to receive an exception like: java.lang.IllegalArgumentException: wrong number of arguments and initially when the method is looked up and invoked for a few times, it does throw that correct error. Here's an example stacktrace which has the correct exception message:

Exception in thread "main" java.lang.IllegalArgumentException: wrong number of arguments
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.myapp.ReflectionMethodInvokerBugTest.main(ReflectionMethodInvokerBugTest.java:20)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)




However, the issues starts to appear when the method has been looked up via reflection and invoked upon for a good number of times. So after a period of "warm up" (I could reproduce it consistently after 500 lookups and invocations) if I do the same steps as above, it runs into a NPE like this:

Exception in thread "main" java.lang.IllegalArgumentException: java.lang.NullPointerException@4769b07b
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.myapp.ReflectionMethodInvokerBugTest.main(ReflectionMethodInvokerBugTest.java:20)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

Notice that the exception that's now thrown is java.lang.IllegalArgumentException: java.lang.NullPointerException@4769b07b and also notice that the stacktrace now shows that the method invocation is now being handled by what appears to be a dynamically generated internal JRE class:

at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)


The simple program to reproduce this is available in the source code section of this bug report.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the code that's shown in the source code section of this bug

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The exception thrown should include the correct exception message which is - java.lang.IllegalArgumentException: wrong number of arguments
ACTUAL -
java.lang.IllegalArgumentException: java.lang.NullPointerException@4769b07b

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------

package org.myapp;

import java.lang.reflect.Method;

/**
 * @author Jaikiran Pai
 */
public class ReflectionMethodInvokerBugTest {

    public static void main(String[] args) throws Exception {
        final ReflectionMethodInvokerBugTest self = new ReflectionMethodInvokerBugTest();
        // This count is used to decide when to pass an invalid number of arguments to the method during the reflection call.
        // This should be sufficiently high to reproduce the NPE, since the JRE generates the dynamic (internal) method invoker
        // after the method has been invoked a good number of times.
        final int warmupCount = 500;
        for (int i = 0; i < 1000; i++) {
            final Method method = self.getClass().getMethod("doSomething", String.class);
            if (i > warmupCount) {
                // intentionally pass wrong argument
                method.invoke(self, null);
            } else {
                method.invoke(self, "test-" + i);
            }
        }

    }

    public void doSomething(final String foo) {
        System.out.println(foo);
    }
}

---------- END SOURCE ----------