[fix] Make static fields private

Author: hazendaz

src/main/java/org/apache/ibatis/io/VFS.java

@@ -36,12 +36,12 @@ public abstract class VFS {
   private static final Log log = LogFactory.getLog(VFS.class);
 
   /** The built-in implementations. */
-  public static final Class<?>[] IMPLEMENTATIONS = { JBoss6VFS.class, DefaultVFS.class };
+  private static final Class<?>[] IMPLEMENTATIONS = { JBoss6VFS.class, DefaultVFS.class };
 
   /**
    * The list to which implementations are added by {@link #addImplClass(Class)}.
    */
-  public static final List<Class<? extends VFS>> USER_IMPLEMENTATIONS = new ArrayList<>();
+  private static final List<Class<? extends VFS>> USER_IMPLEMENTATIONS = new ArrayList<>();
 
   /** Singleton instance holder. */
   private static class VFSHolder {