Two pack APIs are available to the user:

pack(java.util.jar.JarFile in , java.io.OutputStream out)
pack(java.util.jar.JarInputStream in, java.io.OutputStream out)

They do not produce the same output as the following code and output shows:

public static void main(String[] args){

        Pack200 p200 = new Pack200();
        Map p = p200.getProperties();
// p.put(Pack200.PACK_EFFORT,"3");
        p.put("pack.modification.time","latest");
        System.out.println(p200);

// perform a pack cycle using Streams
        try {
                // Call the packer
                JarInputStream jistream = new JarInputStream(new FileInputStream("test.jar"));
                FileOutputStream fostream = new FileOutputStream("test.pack");
                p200.pack(jistream, fostream);
                fostream.close();
                // Call the unpacker
                FileInputStream fistream = new FileInputStream("test.pack");
                JarOutputStream jostream = new JarOutputStream(new FileOutputStream("test_unpacked.jar"));
                p200.unpack(fistream, jostream);
                jostream.close();
            } catch (IOException ioe) {
                ioe.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }

// perform a pack cycle using File
        try {
                // Call the packer
                JarFile jarFile = new JarFile("test.jar");
                FileOutputStream fostream2 = new FileOutputStream("test2.pack");
                p200.pack(jarFile, fostream2);
                fostream2.close();
                // Call the unpacker
                File file = new File("test2.pack");
                JarOutputStream jostream2 = new JarOutputStream(new FileOutputStream("test2_unpacked.jar"));
                p200.unpack(file, jostream2);
                jostream2.close();
            } catch (IOException ioe) {
                ioe.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

which produces:
-rwxrwxrwx 1 kb144018 green 1602590 Oct 11 17:22 test.jar*
-rw-rw-rw- 1 kb144018 green 1486955 Oct 12 02:13 test.pack
-rw-rw-rw- 1 kb144018 green 1587169 Oct 12 02:14 test2.pack
-rw-rw-rw- 1 kb144018 green 1602397 Oct 12 02:14 test2_unpacked.jar
-rw-rw-rw- 1 kb144018 green 1602276 Oct 12 00:54 test_unpacked.jar

test.pack (result of the stream pack method) is different from test2.pack (result of the File pack method).

Even if the unpacked jars are different, a separate experiment showed that
the file and stream unpack method produce the same output given the same
input pack file.