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Bug 342796

Summary:	Use of <? extends MyClass>
Product:	[Eclipse Project] JDT	Reporter:	danielbackman38
Component:	Core	Assignee:	Srikanth Sankaran <srikanth_sankaran>
Status:	VERIFIED INVALID	QA Contact:
Severity:	enhancement
Priority:	P3	CC:	amj87.iitr, srikanth_sankaran
Version:	3.6.2
Target Milestone:	3.7 M7
Hardware:	PC
OS:	Windows 7
Whiteboard:

Description danielbackman38

2011-04-14 03:33:45 EDT

When i try to use <? extends MyClass> in a List I get a compilation error for inserting subclasses to MyClass. If i switch to <? super MyClass> the compilation
error disappears. It seams to be that the compiler thinks backwards :)


-- Configuration Details --
Product: Eclipse 1.3.2.20110218-0812 (org.eclipse.epp.package.jee.product)
Installed Features:
 org.eclipse.jdt 3.6.2.r362_v20101117-0800-7z8XFW6FLFlmjJcvz03jyeFBLS_F

Comment 1 Walter Harley

2011-04-14 04:21:19 EDT

Please include some sample code that you believe should compile but that does not.

Comment 2 Srikanth Sankaran

2011-04-14 05:17:23 EDT

Please also check the behavior with javac against your code.

Comment 3 Srikanth Sankaran

2011-04-20 02:37:42 EDT

I presume your test case looks something like:

import java.util.List;

public class X {
	public static void foo(List<? extends X> p, List <? super X> q) {
            p.add(new X()); // ERROR
	    q.add(new X()); // OK
	}
}

and p.add generates an error while q.add doesn't. This is the intended
behavior. To see why consider p to be assigned a actual parameter that
is a List<Y> where Y extends X. Allowing addition to X's to such a list
would break type safety.

Please reopen with a full test case if this is not the issue.

Comment 4 Ayushman Jain

2011-04-25 06:05:20 EDT

Verified for 3.7M7.