The modifier mask for fields and methods is similar but not exactly the same. The decompiler is most likely using the toString method here
http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/lang/reflect/Modifier.java
but what it doesn't do is handle all bits
// Bits not (yet) exposed in the public API either because they
// have different meanings for fields and methods and there is no
// way to distinguish between the two in this class, or because
// they are not Java programming language keywords
What its doesn't handle is the bits which can mean synthetic and bridge which identify compiler generated code.
If volatile means anything at all here, it could mean don't remove the method even though it doesn't do anything.
