FileWriter object failed to close when UTF-16 encoding used and FileWriter object was initialized with FileDescriptor of closed FileOutputStream object. With UTF-8 encoding test below passed.

import java.io.*;

public class TestFW {

    static byte[] bytes = {0, 2, 4, 6, 8};


    /**
     * This method constructs FileWriter with FileDescriptor object of a
     * file which is instantiated, exists or not exists.
     * if exists, it is readable, open, non-empty)
     * Returns the constructed object.
     * @param fd FileDescriptor of the file
     * @return Status Status of the test
     */
    
    public static void main (String[] args) {
        

        try {
            File tmp = File.createTempFile("test", "fw");
            FileOutputStream fos = new FileOutputStream(tmp);
            fos.write(bytes);
            FileDescriptor fd = fos.getFD();
            fos.close(); //To pass with UTF-16 comment this line and uncomment fos.close() below
            System.out.println("fd.valid()=" + fd.valid());
            System.out.println("Constructing FileWriter( FileDescriptor )");
            FileWriter fw = new FileWriter(fd);
            System.out.println("Encoding: " + fw.getEncoding());
            System.out.println("Constructor successful");
            fw.close();
            System.out.println("FileWriter closed");
            fos.close();//uncomment this to pass with UTF-16
        }
        catch (SecurityException e) {
            System.out.println("Test bypassed. File creation disallowed due to "
                        +"exception "+e);
            System.out.println("OKAY");
        }
        catch (IOException e) {
            e.printStackTrace(System.out);
            System.out.println("Unexpected exception during flush/close: "+e);
        }

    }
}

Output of java -cp. -Dfile.encoding=UTF-16 TestFW with closed descriptor:

   f d . v a l i d ( ) = f a l s e
 C o n s t r u c t i n g F i l e W r i t e r ( F i l e D e s c r i p t o r )
 E n c o d i n g : U T F - 1 6
 C o n s t r u c t o r s u c c e s s f u l
 j a v a . i o . I O E x c e p t i o n : N o s u c h f i l e o r d i r e c t o r y
         a t j a v a . i o . F i l e O u t p u t S t r e a m . w r i t e B y t e s ( N a t i v e M e t h o d )
         a t j a v a . i o . F i l e O u t p u t S t r e a m . w r i t e ( U n k n o w n S o u r c e )
         a t s u n . n i o . c s . S t r e a m E n c o d e r $ C h a r s e t S E . w r i t e B y t e s ( U n k n o w n
   S o u r c e )
         a t s u n . n i o . c s . S t r e a m E n c o d e r $ C h a r s e t S E . i m p l C l o s e ( U n k n o w n
 S o u r c e )
         a t s u n . n i o . c s . S t r e a m E n c o d e r . c l o s e ( U n k n o w n S o u r c e )
         a t j a v a . i o . O u t p u t S t r e a m W r i t e r . c l o s e ( U n k n o w n S o u r c e )
         a t T e s t F W . m a i n ( T e s t F W . j a v a : 3 1 )
 U n e x p e c t e d e x c e p t i o n d u r i n g f l u s h / c l o s e : j a v a . i o . I O E x c e p t i o n
 : N o s u c h f i l e o r d i r e c t o r y

Output of java -cp. -Dfile.encoding=UTF-8 TestFW with closed descriptor:

fd.valid()=false
Constructing FileWriter( FileDescriptor )
Encoding: UTF8
Constructor successful
FileWriter closed

Output of java -cp. -Dfile.encoding=UTF-16 TestFW with not closed descriptor:

   f d . v a l i d ( ) = t r u e
 C o n s t r u c t i n g F i l e W r i t e r ( F i l e D e s c r i p t o r )
 E n c o d i n g : U T F - 1 6
 C o n s t r u c t o r s u c c e s s f u l
 F i l e W r i t e r c l o s e d