content: import org.opencv.core.Core;
  import org.opencv.core.Mat;
  import org.opencv.core.MatOfKeyPoint;
  import org.opencv.features2d.Features2d;
  import org.opencv.highgui.HighGui;
  import org.opencv.imgcodecs.Imgcodecs;
  import org.opencv.xfeatures2d.SURF;
  
  class SURFDetection {
      public void run(String[] args) {
          String filename = args.length > 0 ? args[0] : "../data/box.png";
          Mat src = Imgcodecs.imread(filename, Imgcodecs.IMREAD_GRAYSCALE);
          if (src.empty()) {
              System.err.println("Cannot read image: " + filename);
              System.exit(0);
          }
  
          //-- Step 1: Detect the keypoints using SURF Detector
          double hessianThreshold = 400;
          int nOctaves = 4, nOctaveLayers = 3;
          boolean extended = false, upright = false;
          SURF detector = SURF.create(hessianThreshold, nOctaves, nOctaveLayers, extended, upright);
          MatOfKeyPoint keypoints = new MatOfKeyPoint();
          detector.detect(src, keypoints);
  
          //-- Draw keypoints
          Features2d.drawKeypoints(src, keypoints, src);
  
          //-- Show detected (drawn) keypoints
          HighGui.imshow("SURF Keypoints", src);
          HighGui.waitKey(0);
  
          System.exit(0);
      }
  }
  
  public class SURFDetectionDemo {
      public static void main(String[] args) {
          // Load the native OpenCV library
          System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
  
          new SURFDetection().run(args);
      }
  }
  