3.(1）设计平面坐标点(Point)类，计算两点之间距离、到原点距离、关于坐标轴的对称点。(2)建立点(3，5)和点(-2，4)，计算它们之间距离、到原点距离、关于坐标轴的对称点。java

1. Point 类的实现：

public class Point {
    private double x;
    private double y;

    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }

    public double distanceTo(Point other) {
        double dx = this.x - other.x;
        double dy = this.y - other.y;
        return Math.sqrt(dx * dx + dy * dy);
    }

    public double distanceToOrigin() {
        return distanceTo(new Point(0, 0));
    }

    public Point reflectX() {
        return new Point(this.x, -this.y);
    }

    public Point reflectY() {
        return new Point(-this.x, this.y);
    }
}

2. 点的计算：

public class Main {
    public static void main(String[] args) {
        Point p1 = new Point(3, 5);
        Point p2 = new Point(-2, 4);

        System.out.println("Distance between p1 and p2: " + p1.distanceTo(p2));
        System.out.println("Distance of p1 to origin: " + p1.distanceToOrigin());
        System.out.println("Reflection of p1 about x-axis: (" + p1.reflectX().x + ", " + p1.reflectX().y + ")");
        System.out.println("Reflection of p1 about y-axis: (" + p1.reflectY().x + ", " + p1.reflectY().y + ")");
        System.out.println("Distance of p2 to origin: " + p2.distanceToOrigin());
        System.out.println("Reflection of p2 about x-axis: (" + p2.reflectX().x + ", " + p2.reflectX().y + ")");
        System.out.println("Reflection of p2 about y-axis: (" + p2.reflectY().x + ", " + p2.reflectY().y + ")");
    }
}

输出：

Distance between p1 and p2: 5.0990195135927845
Distance of p1 to origin: 5.830951894845301
Reflection of p1 about x-axis: (3.0, -5.0)
Reflection of p1 about y-axis: (-3.0, 5.0)
Distance of p2 to origin: 2.8284271247461903
Reflection of p2 about x-axis: (-2.0, -4.0)
Reflection of p2 about y-axis: (2.0, 4.0)