8342083: Make a few fields in FileSystemPreferences final

Reviewed-by: jpai, bpb

src/java.prefs/unix/classes/java/util/prefs/FileSystemPreferences.java

@@ -450,7 +450,7 @@ private void replayChanges() {
             changeLog.get(i).replay();
     }
 
-    private static Timer syncTimer = new Timer(true); // Daemon Thread
+    private static final Timer syncTimer = new Timer(true); // Daemon Thread
 
     static {
         addShutdownHook();
@@ -540,7 +540,7 @@ public Void run() {
             }
         });
         if (newNode) {
-            // These 2 things guarantee node will get wrtten at next flush/sync
+            // These 2 things guarantee node will get written at next flush/sync
             prefsCache = new TreeMap<>();
             nodeCreate = new NodeCreate();
             changeLog.add(nodeCreate);
@@ -1008,12 +1008,12 @@ private void checkLockFile0ErrorCode (int errorCode)
      * Initial time between lock attempts, in ms.  The time is doubled
      * after each failing attempt (except the first).
      */
-    private static int INIT_SLEEP_TIME = 50;
+    private static final int INIT_SLEEP_TIME = 50;
 
     /**
      * Maximum number of lock attempts.
      */
-    private static int MAX_ATTEMPTS = 5;
+    private static final int MAX_ATTEMPTS = 5;
 
     /**
      * Release the appropriate file lock (user or system).