(The MyPoint class) Design a class named MyPoint to represent a point with x- and y-coordinates. The class contains: ■ The data fields x and y that represent the coordinates with getter methods. ■ A no-arg constructor that creates a point (0, 0). ■ A constructor that constructs a point with specified coordinates. ■ A method named distance that returns the distance from this point to a specified point of the MyPoint type. ■ A method named distance that returns the distance from this point to another point with specified x- and y-coordinates. Draw the UML diagram for the class and then implement the class. Write a test program that creates the two points (0, 0) and (10, 30.5) and displays the distance between them.

下面是 MyPoint 类的 UML 图和实现代码：

public class MyPoint {
    private double x;
    private double y;
    
    public MyPoint() {
        this(0, 0);
    }
    
    public MyPoint(double x, double y) {
        this.x = x;
        this.y = y;
    }
    
    public double getX() {
        return x;
    }
    
    public double getY() {
        return y;
    }
    
    public double distance(MyPoint point) {
        double dx = this.x - point.x;
        double dy = this.y - point.y;
        return Math.sqrt(dx * dx + dy * dy);
    }
    
    public double distance(double x, double y) {
        return distance(new MyPoint(x, y));
    }
}

测试程序如下：

public class TestMyPoint {
    public static void main(String[] args) {
        MyPoint p1 = new MyPoint();
        MyPoint p2 = new MyPoint(10, 30.5);
        System.out.println("Distance between (" + p1.getX() + ", " + p1.getY() 
                           + ") and (" + p2.getX() + ", " + p2.getY() 
                           + ") is " + p1.distance(p2));
    }
}

输出：

Distance between (0.0, 0.0) and (10.0, 30.5) is 32.09750769140807