code: public long getLastModified() {
          final SecurityManager sm = System.getSecurityManager();
          if (sm != null) {
              sm.checkPermission(new VirtualFilePermission(getPathName(), "read"));
          }
          final VFS.Mount mount = VFS.getMount(this);
          if (sm != null) {
              return AccessController.doPrivileged(
                      (PrivilegedAction<Long>) () -> mount.getFileSystem().getLastModified(mount.getMountPoint(), this)
              );
          }
          return mount.getFileSystem().getLastModified(mount.getMountPoint(), this);
      }
docs: When the file was last modified
  
  @return the last modified time