计算直角坐标系中，两点之间距离、两条直线之间的交点坐标、某点是否在某条直线上。

两点之间距离，该方法遵循公式：

Point p1 = new Point(5, 6);// 定义第一个点的坐标(5,6)
        Point p2 = new Point(7, 8);// 定义第二个点的坐标(7,8)
        //定位坐标
        System.out.println("p1的x坐标为" + p1.getX());
        System.out.println("p1的y坐标为" + p1.getY());
        System.out.println("p2的x坐标为" + p2.getX());
        System.out.println("p2的y坐标为" + p2.getY());
        // 计算两点间距离公式
        double juli = Math.sqrt(Math.abs((p1.getX() - p2.getX()) * (p1.getX() - p2.getX()) + (p1.getY() - p2.getY()) * (p1.getY() - p2.getY())));
        System.out.println("两点间的距离是:" + juli);

 两点之间的交点坐标，遵循公式：

@Getter
@Setter
public class Lseg {

    public Lseg(Light.Point startPoint, Light.Point endPoint) {
        this.startPoint = startPoint;
        this.endPoint = endPoint;
    }

    private Light.Point startPoint;

    private Light.Point endPoint;
}

/**
     * 获取两条线之间的交点
     * @param lsegA 起点
     * @param lsegB 终点
     */
    public static Light.Point getCrossPoint(Lseg lsegA, Lseg lsegB) {
        double x;
        double y;
        double x1 = lsegA.getStartPoint().getX();
        double y1 = lsegA.getStartPoint().getY();
        double x2 = lsegA.getEndPoint().getX();
        double y2 = lsegA.getEndPoint().getY();
        double x3 = lsegB.getStartPoint().getX();
        double y3 = lsegB.getStartPoint().getY();
        double x4 = lsegB.getEndPoint().getX();
        double y4 = lsegB.getEndPoint().getY();
        double k1 = Float.MAX_VALUE;
        double k2 = Float.MAX_VALUE;
        boolean flag1 = false;
        boolean flag2 = false;

        if ((x1 - x2) == 0)
            flag1 = true;
        if ((x3 - x4) == 0)
            flag2 = true;

        if (!flag1)
            k1 = (y1 - y2) / (x1 - x2);
        if (!flag2)
            k2 = (y3 - y4) / (x3 - x4);

        if (k1 == k2)
            return null;

        if (flag1) {
            if (flag2)
                return null;
            x = x1;
            if (k2 == 0) {
                y = y3;
            } else {
                y = k2 * (x - x4) + y4;
            }
        } else if (flag2) {
            x = x3;
            if (k1 == 0) {
                y = y1;
            } else {
                y = k1 * (x - x2) + y2;
            }
        } else {
            if (k1 == 0) {
                y = y1;
                x = (y - y4) / k2 + x4;
            } else if (k2 == 0) {
                y = y3;
                x = (y - y2) / k1 + x2;
            } else {
                x = (k1 * x2 - k2 * x4 + y4 - y2) / (k1 - k2);
                y = k1 * (x - x2) + y2;
            }
        }
        if (between(x1, x2, x) && between(y1, y2, y) && between(x3, x4, x) && between(y3, y4, y)) {
            Light.Point point = new Light.Point();
            point.setX(x);
            point.setY(y);
            if (point.equals(lsegA.getStartPoint()) || point.equals(lsegA.getEndPoint()))
                return null;
            return point;
        } else {
            return null;
        }
    }

    public static boolean between(double a, double b, double target) {
        if (target >= a - 0.01 && target <= b + 0.01 || target <= a + 0.01 && target >= b - 0.01)
            return true;
        else
            return false;
    }

 @Test
    void test01() {
        Light.Point point1 = new Light.Point();
        point1.setX(1);
        point1.setY(1);
        Light.Point point2 = new Light.Point();
        point2.setX(5);
        point2.setY(5);
        Lseg lseg = new Lseg(point1, point2);
        Light.Point point3 = new Light.Point();
        point3.setX(1);
        point3.setY(5);
        Light.Point point4 = new Light.Point();
        point4.setX(5);
        point4.setY(1);
        Lseg lseg1 = new Lseg(point3, point4);
        Light.Point point = getCrossPoint(lseg, lseg1);
        System.out.println("直线A 坐标为 1,1  5,5");
        System.out.println("直线B 坐标为 1,5  5,1");
        System.out.println("两线之间的交点为 " + point.getX() + "，" + point.getY());
    }

某点是否在某条直线上，遵循公式：

（Q-P1）*（P1-P2）=0 即三点共线

@Getter
@Setter
public class LineVo {

    public LineVo(Light.Point startPoint, Light.Point endPoint) {
        this.startPoint = startPoint;
        this.endPoint = endPoint;
    }

    private Light.Point startPoint;

    private Light.Point endPoint;
}

 /**
     * 判断某点是否在一条直线上
     *
     * @param lineVo 线
     * @param point  点
     */
    public static boolean flagOnLine(LineVo lineVo, Light.Point point) {
        if (((point.getX() - lineVo.getStartPoint().getX()) * (lineVo.getStartPoint().getY() - lineVo.getEndPoint().getY()))
                == ((lineVo.getStartPoint().getX() - lineVo.getEndPoint().getX()) * (point.getY() - lineVo.getStartPoint().getY()))
                && (point.getX() >= Math.min(lineVo.getStartPoint().getX(), lineVo.getEndPoint().getX())
                && point.getX() <= Math.max(lineVo.getStartPoint().getX(), lineVo.getEndPoint().getX()))
                && ((point.getY() >= Math.min(lineVo.getStartPoint().getY(), lineVo.getEndPoint().getY()))
                && (point.getY() <= Math.max(lineVo.getStartPoint().getY(), lineVo.getEndPoint().getY())))) {
            return true;
        } else {
            return false;
        }
    }

@Test
    void test02() {
        LinePoint startPoint = new LinePoint();
        startPoint.setXCoordinates(19d);
        startPoint.setYCoordinates(25d);
        LinePoint endPoint = new LinePoint();
        endPoint.setXCoordinates(19d);
        endPoint.setYCoordinates(30d);
        LineVo lineVo1 = new LineVo(startPoint, endPoint);
        Light.Point point = new Light.Point();
        point.setX(19);
        point.setY(26);
        Assert.isTrue(LineCalculateUtil.flagOnLine(lineVo1, point), "不在一条线上");
    }