What is the meaning of "non-opaque values" in Java 7?

Question

Java 7's AttributeView will let you create and update non-opaque values associated with objects in a file system. What does that mean?

Answer 1

Opaque values are abstract items that you can pass around but can't see or change. A good example is a file handle provided by the operating system - you can get one and pass it to other functions that require a file handle, but you have no way of knowing what it actually is.

For example, an opaque value of a file might be the physical location of the home block of the file on a disk - something which exists, but which you are not allowed to read or write.