A DESCRIPTION OF THE REQUEST :
a call to File.isHidden costs a call to getBooleanAttributes, even on Unix:

    public boolean isHidden() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkRead(path);
        }
        return ((fs.getBooleanAttributes(this) & FileSystem.BA_HIDDEN) != 0);
    }

it should end:

  return fs.isHidden(this);

and UnixFileSystem should change like this:

+ public boolean isHidden(File f) {
+ return f.getName().startsWith(".");
+ }

    public int getBooleanAttributes(File f) {
- int rv = getBooleanAttributes0(f);
+ return getBooleanAttributes0(f);
- String name = f.getName();
- boolean hidden = (name.length() > 0) && (name.charAt(0) == '.');
- return rv | (hidden ? BA_HIDDEN : 0);
    }

(or you could just make getBooleanAttributes the native method, as with the Win(32|NT)FileSystem classes.)

JUSTIFICATION :
getBooleanAttributes is pretty slow. if you're scanning a large file system, and trying to ignore hidden files in a platform-independent way, the calls to getBooleanAttributes can take 10% of your time, for nothing. this encourages Unix developers to ditch File.isHidden in favor of startsWith("."), and Windows users potentially lose out.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
i'd like to see File.isHidden cost no more on Unix than startsWith("."), but still do the right thing on Windows. one shouldn't pay for what one doesn't use.
ACTUAL -
Unix users pay for getBooleanAttributes, the JNI transition, and the stat(2), all for nothing.

CUSTOMER SUBMITTED WORKAROUND :
calling startsWith(".") instead of File.isHidden, but that sucks for Windows users, as if their lives weren't bad enough already.