检查Java Swing中的点是否在线

   private int pointX;

   private int pointY;

   public PointOnlineCheck() {

       setSize(400, 400);

       setVisible(true);

       addMouseListener(new MouseAdapter() {

           public void mouseClicked(MouseEvent e) {

               pointX = e.getX();

               pointY = e.getY();

               repaint();

           }

       });

   }

   public void paint(Graphics g) {

       super.paint(g);

       g.setColor(Color.RED);

       g.fillOval(pointX - 5, pointY - 5, 10, 10);

       int x1 = 100;  // 直线上的点A的x坐标

       int y1 = 100;  // 直线上的点A的y坐标

       int x2 = 300;  // 直线上的点B的x坐标

       int y2 = 300;  // 直线上的点B的y坐标

       int x = pointX;  // 待判断的点C的x坐标

       int y = pointY;  // 待判断的点C的y坐标

       // 计算点C到直线AB的距离

       double distance = Math.abs((y2 - y1) * x - (x2 - x1) * y + x2 * y1 - y2 * x1) / Math.sqrt(Math.pow(y2 - y1, 2) + Math.pow(x2 - x1, 2));

       if (distance == 0) {

           g.drawString("点在线上", 150, 350);

       } else {

           g.drawString("点不在线上", 150, 350);

       }

   }

   public static void main(String[] args) {

       new PointOnlineCheck();

   }