JDK-6506307 : (reflect) Method.getReturnType() returns wrong type for overriding methods (generics)
  • Type: Bug
  • Component: tools
  • Sub-Component: javac
  • Affected Version: 6
  • Priority: P4
  • Status: Closed
  • Resolution: Duplicate
  • OS: windows_xp
  • CPU: x86
  • Submitted: 2006-12-19
  • Updated: 2010-05-09
  • Resolved: 2007-01-03
Related Reports
Duplicate :  
Description
FULL PRODUCT VERSION :
java version "1.6.0"
Java(TM) SE Runtime Environment (build 1.6.0-b105)
Java HotSpot(TM) Client VM (build 1.6.0-b105, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
Consider the following examples classes:

public class Example1<E extends Collection> {
  public E process(){...}
}
 
public class Example2 extends Example1<List> {}

Calling Example2.getMethod("process").getReturnType() returns 'java.util.Collection' and not, as expected 'java.util.List'.

As class Example2 itself is not generic I consider this inaccurate.

Note: I already reported this bug against JDK 1.5.0 but never got an answer.

The following (legal) code examples illustrates that the return type of Example2.process() is obviously 'List' and not 'Collection':

public class Example3 {
  public void test() {
    Example2 example2 = new Example2();
    List test = example2.process();
  }
}

This problem was already discussed in http://forum.java.sun.com/thread.jspa?threadID=707880

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
See description or use example code below.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I would expect Example2.getMethod("process").getReturnType()  to return 'java.util.List' (see description).
ACTUAL -
Actual result is 'java.util.Collection'  (the lower bound of generic parameter E in class 'Example1'. If the class does not have a lower bound, 'java.lang.Object' is returned.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.Collection;
import java.util.List;

public class ReflectionBugDemo {
  public static void main(String[] args) throws SecurityException, NoSuchMethodException {
    Class<?> returnType1 = Example1.class.getMethod("process").getReturnType();
    Class<?> returnType2 = Example2.class.getMethod("process").getReturnType();
    
    System.out.println("Return type of Example1.process(): " +returnType1);
    System.out.println("Return type of Example2.process(): " +returnType2);
  }
  
}

class Example1<E extends Collection> {
  public E process() {
    return null;
  }
}

class Example2 extends Example1<List> {}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
There was a workround presented in http://forum.java.sun.com/thread.jspa?threadID=707880 but these (and other solution I found myself) are extremely cumbersome.