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Bug ID: 6219964 Compiler allows illegal cast of anonymous inner class
6219964 : Compiler allows illegal cast of anonymous inner class

Details
Type:
Bug
Submit Date:
2005-01-21
Status:
Closed
Updated Date:
2010-04-02
Project Name:
JDK
Resolved Date:
2005-09-30
Component:
tools
OS:
windows_xp
Sub-Component:
javac
CPU:
x86
Priority:
P3
Resolution:
Fixed
Affected Versions:
5.0
Fixed Versions:
6

Related Reports
Relates:
JDK-6520152 - ACC_FINAL flag for anonymous classes shouldn't be set
Relates:
JDK-7064370 - Anonymous inner class in incorrectly non-public
Relates:
JDK-4916620 - legal cast is rejected

Sub Tasks

Description
FULL PRODUCT VERSION :
java version "1.5.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-b64)
Java HotSpot(TM) Client VM (build 1.5.0-b64, mixed mode)

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

A DESCRIPTION OF THE PROBLEM :
The following source code compiles although it should be rejected because the anonymous inner class doesn't implement the interface Test231i and therefore it is illegal to cast the this pointer of the anonymous inner class to the interface:

class Test231 implements Test231i
{
	void	foo()
	{
		new Object()
		{
			Test231i	bar()
			{
				return	(Test231i)this;
			}
		};
	}
}


interface Test231i
{
}

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile  the example given in the description with javac.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Compilation should fail with an error message.
ACTUAL -
No errors are reported by javac.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
class Test231 implements Test231i
{
	void	foo()
	{
		new Object()
		{
			Test231i	bar()
			{
				return	(Test231i)this;
			}
		};
	}
}


interface Test231i
{
}
---------- END SOURCE ----------
###@###.### 2005-1-21 06:52:01 GMT

Comments
WORK AROUND

The cast will always fail at run time.  The programmer almost certainly
meant:
 
                return (Test231i)Test231.this;
2005-09-26 
EVALUATION

The submitter is correct.  Quoting the JLS:

15.9.5 Anonymous Class Declarations:
... "An anonymous class is always implicitly final (8.1.1.2)."

5.5 Casting Conversion
... "compile-time reference type S (source) to a compile-time reference
type T (target)." ...
... "If T is an interface type" ...
"If S is a final class (8.1.1), then S must implement T, or a compile-time
error occurs."

The problem appears to be that the compiler don't mark anonymous classes
final.

###@###.### 2005-1-21 09:21:15 GMT

We should fix this in mustang.  No apparent need for backport to JDK 5.

###@###.### 2005-1-21 20:05:33 GMT
2005-01-21 
SUGGESTED FIX

Index: src/share/classes/com/sun/tools/javac/comp/Check.java
============================================================
@@ -597,9 +597,13 @@
 	case TYP:
 	    if (sym.isLocal()) {
 		mask = LocalClassFlags;
+		if (sym.name.len == 0) { // Anonymous class
 		// Anonymous classes in static methods are themselves static;
 		// that's why we admit STATIC here.
-		if (sym.name.len == 0) mask |= STATIC;
+		    mask |= STATIC;
+		    // JLS: Anonymous classes are final.
+		    implicit |= FINAL;
+		}
 		if ((sym.owner.flags_field & STATIC) == 0 &&
 		    (flags & ENUM) != 0)
                     log.error(pos, "enums.must.be.static");

###@###.### 2005-1-21 19:58:58 GMT
2005-01-21


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