I have opened a PrintWriter and the used that as target to the formatter, any format operation after it was properly closed.
should throw an exception.
It throws FormatterClosedException in case of Append method, but not on this

The following is the example code and how it works on console.
import java.util.*;
import java.io.*;
public class Test {
    public static void main(String[] arg) {
    try {
    PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("foo.out")));
    Formatter formatter = new Formatter(out);
    out.println(" In side the file.. ");
    out.flush();
    out.close(); // writer closed.

    formatter.format(" %20d is a nunmber",20);

    } catch(Exception ioe) {
        ioe.printStackTrace();
    }
    }
}
console :-
vishalb:/home/vv145429/tiger/src/formating/bugs 55 % javac -source 1.5 Test.java
vishalb:/home/vv145429/tiger/src/formating/bugs 56 % java Test
vishalb:/home/vv145429/tiger/src/formating/bugs 57 % cat foo.out
 In side the file..
vishalb:/home/vv145429/tiger/src/formating/bugs 58 %