code: public long classpathContentsLastModifiedTime() {
          if (closed.get()) {
              throw new IllegalArgumentException("Cannot use a ScanResult after it has been closed");
          }
          long maxLastModifiedTime = 0L;
          if (fileToLastModified != null) {
              final long currTime = System.currentTimeMillis();
              for (final long timestamp : fileToLastModified.values()) {
                  if (timestamp > maxLastModifiedTime && timestamp < currTime) {
                      maxLastModifiedTime = timestamp;
                  }
              }
          }
          return maxLastModifiedTime;
      }
docs: Find the maximum last-modified timestamp of any whitelisted file/directory/jarfile encountered during the
  scan. Checks the current timestamps, so this should increase between calls if something changes in
  whitelisted paths. Assumes both file and system timestamps were generated from clocks whose time was
  accurate. Ignores timestamps greater than the system time.
  
  <p>
  This method cannot in general tell if classpath has changed (or modules have been added or removed) if it is
  run twice during the same runtime session.
  
  @return the maximum last-modified time for whitelisted files/directories/jars encountered during the scan.