1.设计一个Point类表示平面坐标系中的点。该类包括私有的double型的x和y属性。两个构造方法，一个是无参的构造方法，该方法中×和y的值为0；另外一个构造方法包含两个参数，分别为x和y赋值。为x和y属性提供 setter和getter方法，重写Object类的hashcode和equals方法。最后重写Object类的toString()方法。 编写一个类，包含如下功能：（1）定义一个数组，数组的长度是 50，数组元素是Point的对象。Point对象的x和y值随机赋值。 (2)判断数组中是否有两个相等的点(点的x和y的值相等) (3)指定一个点，求该点到其他点的距离(两种理解) (4)求距离最近的两个点。

Point类的代码如下：

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

    public Point() {
        this.x = 0;
        this.y = 0;
    }

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

    public double getX() {
        return x;
    }

    public void setX(double x) {
        this.x = x;
    }

    public double getY() {
        return y;
    }

    public void setY(double y) {
        this.y = y;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        long temp;
        temp = Double.doubleToLongBits(x);
        result = prime * result + (int) (temp ^ (temp >>> 32));
        temp = Double.doubleToLongBits(y);
        result = prime * result + (int) (temp ^ (temp >>> 32));
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Point other = (Point) obj;
        if (Double.doubleToLongBits(x) != Double.doubleToLongBits(other.x))
            return false;
        if (Double.doubleToLongBits(y) != Double.doubleToLongBits(other.y))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "Point [x=" + x + ", y=" + y + "]";
    }
}

基于Point类，实现包含如下功能的类：

import java.util.Random;

public class PointArray {
    private Point[] points;

    public PointArray() {
        this.points = new Point[50];
        Random random = new Random();
        for (int i = 0; i < 50; i++) {
            double x = random.nextDouble() * 100;
            double y = random.nextDouble() * 100;
            points[i] = new Point(x, y);
        }
    }

    public boolean hasEqualPoints() {
        for (int i = 0; i < points.length - 1; i++) {
            for (int j = i + 1; j < points.length; j++) {
                if (points[i].equals(points[j])) {
                    return true;
                }
            }
        }
        return false;
    }

    public double[] distancesTo(Point p) {
        double[] distances = new double[points.length];
        for (int i = 0; i < points.length; i++) {
            distances[i] = Math.sqrt(Math.pow(points[i].getX() - p.getX(), 2) + Math.pow(points[i].getY() - p.getY(), 2));
        }
        return distances;
    }

    public Point[] closestPoints() {
        Point[] closest = new Point[2];
        double minDistance = Double.MAX_VALUE;
        for (int i = 0; i < points.length - 1; i++) {
            for (int j = i + 1; j < points.length; j++) {
                double distance = Math.sqrt(Math.pow(points[i].getX() - points[j].getX(), 2) + Math.pow(points[i].getY() - points[j].getY(), 2));
                if (distance < minDistance) {
                    minDistance = distance;
                    closest[0] = points[i];
                    closest[1] = points[j];
                }
            }
        }
        return closest;
    }
}

使用示例：

public class Main {
    public static void main(String[] args) {
        PointArray pa = new PointArray();
        System.out.println(pa.hasEqualPoints());

        Point p = new Point(50, 50);
        double[] distances = pa.distancesTo(p);
        for (int i = 0; i < distances.length; i++) {
            System.out.println("distance to point " + i + ": " + distances[i]);
        }

        Point[] closest = pa.closestPoints();
        System.out.println("closest points: " + closest[0] + ", " + closest[1]);
    }
}