content: import java.awt.BorderLayout;
  import java.awt.Container;
  import java.awt.Image;
  
  import javax.swing.BoxLayout;
  import javax.swing.ImageIcon;
  import javax.swing.JFrame;
  import javax.swing.JLabel;
  import javax.swing.JPanel;
  import javax.swing.JSlider;
  import javax.swing.event.ChangeEvent;
  import javax.swing.event.ChangeListener;
  
  import org.opencv.core.Core;
  import org.opencv.core.CvType;
  import org.opencv.core.Mat;
  import org.opencv.core.Point;
  import org.opencv.core.Scalar;
  import org.opencv.highgui.HighGui;
  import org.opencv.imgcodecs.Imgcodecs;
  import org.opencv.imgproc.Imgproc;
  
  class CornerHarris {
      private Mat srcGray = new Mat();
      private Mat dst = new Mat();
      private Mat dstNorm = new Mat();
      private Mat dstNormScaled = new Mat();
      private JFrame frame;
      private JLabel imgLabel;
      private JLabel cornerLabel;
      private static final int MAX_THRESHOLD = 255;
      private int threshold = 200;
  
      public CornerHarris(String[] args) {
          /// Load source image and convert it to gray
          String filename = args.length > 0 ? args[0] : "../data/building.jpg";
          Mat src = Imgcodecs.imread(filename);
          if (src.empty()) {
              System.err.println("Cannot read image: " + filename);
              System.exit(0);
          }
  
          Imgproc.cvtColor(src, srcGray, Imgproc.COLOR_BGR2GRAY);
  
          // Create and set up the window.
          frame = new JFrame("Harris corner detector demo");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          // Set up the content pane.
          Image img = HighGui.toBufferedImage(src);
          addComponentsToPane(frame.getContentPane(), img);
          // Use the content pane's default BorderLayout. No need for
          // setLayout(new BorderLayout());
          // Display the window.
          frame.pack();
          frame.setVisible(true);
          update();
      }
  
      private void addComponentsToPane(Container pane, Image img) {
          if (!(pane.getLayout() instanceof BorderLayout)) {
              pane.add(new JLabel("Container doesn't use BorderLayout!"));
              return;
          }
  
          JPanel sliderPanel = new JPanel();
          sliderPanel.setLayout(new BoxLayout(sliderPanel, BoxLayout.PAGE_AXIS));
  
          sliderPanel.add(new JLabel("Threshold: "));
          JSlider slider = new JSlider(0, MAX_THRESHOLD, threshold);
          slider.setMajorTickSpacing(20);
          slider.setMinorTickSpacing(10);
          slider.setPaintTicks(true);
          slider.setPaintLabels(true);
          slider.addChangeListener(new ChangeListener() {
              @Override
              public void stateChanged(ChangeEvent e) {
                  JSlider source = (JSlider) e.getSource();
                  threshold = source.getValue();
                  update();
              }
          });
          sliderPanel.add(slider);
          pane.add(sliderPanel, BorderLayout.PAGE_START);
  
          JPanel imgPanel = new JPanel();
          imgLabel = new JLabel(new ImageIcon(img));
          imgPanel.add(imgLabel);
  
          Mat blackImg = Mat.zeros(srcGray.size(), CvType.CV_8U);
          cornerLabel = new JLabel(new ImageIcon(HighGui.toBufferedImage(blackImg)));
          imgPanel.add(cornerLabel);
  
          pane.add(imgPanel, BorderLayout.CENTER);
      }
  
      private void update() {
          dst = Mat.zeros(srcGray.size(), CvType.CV_32F);
  
          /// Detector parameters
          int blockSize = 2;
          int apertureSize = 3;
          double k = 0.04;
  
          /// Detecting corners
          Imgproc.cornerHarris(srcGray, dst, blockSize, apertureSize, k);
  
          /// Normalizing
          Core.normalize(dst, dstNorm, 0, 255, Core.NORM_MINMAX);
          Core.convertScaleAbs(dstNorm, dstNormScaled);
  
          /// Drawing a circle around corners
          float[] dstNormData = new float[(int) (dstNorm.total() * dstNorm.channels())];
          dstNorm.get(0, 0, dstNormData);
  
          for (int i = 0; i < dstNorm.rows(); i++) {
              for (int j = 0; j < dstNorm.cols(); j++) {
                  if ((int) dstNormData[i * dstNorm.cols() + j] > threshold) {
                      Imgproc.circle(dstNormScaled, new Point(j, i), 5, new Scalar(0), 2, 8, 0);
                  }
              }
          }
  
          cornerLabel.setIcon(new ImageIcon(HighGui.toBufferedImage(dstNormScaled)));
          frame.repaint();
      }
  }
  
  public class CornerHarrisDemo {
      public static void main(String[] args) {
          // Load the native OpenCV library
          System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
  
          // Schedule a job for the event dispatch thread:
          // creating and showing this application's GUI.
          javax.swing.SwingUtilities.invokeLater(new Runnable() {
              @Override
              public void run() {
                  new CornerHarris(args);
              }
          });
      }
  }
  