On my current project, I've felt the need to create a sort of simulated callback system in Java using reflection. However, I'm having issues getting my reflection to actually function. The code at fault follows:
public Callback(Object parentObj, String methodName, Class<?>...parameters)
{
if(parentObj == null)
throw new IllegalArgumentException("parentObj cannot be null", new NullPointerException());
Class<?> clazz = parentObj.getClass();
// Trace debugging, see output
for(Method m : clazz.getDeclaredMethods())
if(m.getName().equals("myMethod")) System.out.println (m);
try { this.method = clazz.getMethod(methodName, parameters); }
catch(NoSuchMethodException nsme) { nsme.printStackTrace(); } // Exception caught
catch(SecurityException se) { se.printStackTrace(); }
this.parentObj = parentObj;
this.parameters = parameters;
}
When I construct the Callback
object, I'm using syntax like this:
new Callback(this, "myMethod", boolean.class)
When I try to create my pseudo-callback, it hits the NoSuchMethodException
catch block. I've included some trace debugging above to show the output of one of my methods failing. The output:
private void my.package.MyClass.myMethod(boolean)
java.lang.NoSuchMethodException: my.package.MyClass.myMethod(boolean)
at java.lang.Class.getMethod(Class.java:1605)
at my.package.other.Callback.<init>(Callback.java:63)
I couldn't figure the problem out, so I started hunting, to little avail. The best I could find was mention of versioning conflict between the compiled JAR and the runtime. However, MyJar.jar/META-INF/MANIFEST.MF
contains Created-By: 1.6.0_02 (Sun Microsystems Inc.)
. My IDE is running C:\Program Files\Java\jdk1.6.0_02\bin\javac.exe
to compile my project. I'm using C:\Program Files\Java\jdk1.6.0_02\bin\java.exe
to run my JAR.
I'm at a loss why Class.getMethod
is claiming the method doesn't exist, but Class.getMethods
seems to have no problem finding it. Help? :(
Your method is private but getMethod()
only returns public method.
You need to use getDeclaredMethod()
.
Yes! This fixes the problem without forcing me to use public methods. Thanks!
3 years later... That makes a lot of sense in my case. Although I started reading the documentation for both methods at docs.oracle.com/javase/1.5.0/docs/api/java/lang/…, java.lang.Class...) and they don't mention such information. Maybe you looked into the code? Good for you. +1
Was banging my head on the wall for 2 hours straight. Thanks man !
Awesome naming conventions java... how about getPrivateMethod .. lordy
This helped me but in reverse. I had a public method I was trying to call with getDeclaredMethod(), and it didn't find it. Swapped over to getMethod() and it works