【Java Programming】学习笔记-Point2D不能使用问题

Java Programming中的Point2D类

课本上的内容是这样的

import java.util.Scanner;
import javafx.geometry.Point2D;

public class TestPoint2D {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);

		System.out.print("Enter point1's x-, y-coordinates:");
		double x1 = input.nextDouble();
		double y1 = input.nextDouble();
		System.out.print("Enter point2' s x-, y-coordinates:");
		double x2 = input.nextDouble();
		double y2 = input.nextDouble();

		Point2D p1 = new Point2D(x1, y1);
		Point2D p2 = new Point2D(x2, y2);
		System.out.println("p1 is " + p1.toString());
		System.out.println("p2 is " + p2.toString());
		System.out.println("The distance between pi and p2 is" + p1.distance(p1);
	}
}

在eclipse中编译报错，

不仅Point2D类不能实例化，声明都不可以

这是怎么回事呢，经过多次试验，终于发现了问题所在，将上面的导入类javafx.geometry.Point2D换成java.awt.geom.Point2D;
此时便解决了声明问题，但是还是无法实例化。

我找到了java的jdk中的文件

package java.awt.geom;

import java.io.Serializable;

/**
 * The <code>Point2D</code> class defines a point representing a location
 * in {@code (x,y)} coordinate space.
 * <p>
 * This class is only the abstract superclass for all objects that
 * store a 2D coordinate.
 * The actual storage representation of the coordinates is left to
 * the subclass.
 *
 * @author      Jim Graham
 * @since 1.2
 */
public abstract class Point2D implements Cloneable {

    /**
     * The <code>Float</code> class defines a point specified in float
     * precision.
     * @since 1.2
     */
    public static class Float extends Point2D implements Serializable {
        /**
         * The X coordinate of this <code>Point2D</code>.
         * @since 1.2
         * @serial
         */
        public float x;

        /**
         * The Y coordinate of this <code>Point2D</code>.
         * @since 1.2
         * @serial
         */
        public float y;

        /**
         * Constructs and initializes a <code>Point2D</code> with
         * coordinates (0,&nbsp;0).
         * @since 1.2
         */
        public Float() {
        }

        /**
         * Constructs and initializes a <code>Point2D</code> with
         * the specified coordinates.
         *
         * @param x the X coordinate of the newly
         *          constructed <code>Point2D</code>
         * @param y the Y coordinate of the newly
         *          constructed <code>Point2D</code>
         * @since 1.2
         */
        public Float(float x, float y) {
            this.x = x;
            this.y = y;
        }

它的构造函数中有Double， Float，使用的时候只需要用相应的构造函数。。

/** Float type */
System.out.print("Enter point1's x-, y-coordinates:");
		float x1 = input.nextFloat();
		float y1 = input.nextFloat();
		System.out.print("Enter point2' s x-, y-coordinates:");
		float x2 = input.nextFloat();
		float y2 = input.nextFloat();

		Point2D p1 = new Point2D.Float(x1,y1);
		Point2D p2 = new Point2D.Float(x2, y2);

/** Double type */
System.out.print("Enter point1's x-, y-coordinates:");
		double x1 = input.nextDouble();
		double y1 = input.nextDouble();
		System.out.print("Enter point2' s x-, y-coordinates:");
		double x2 = input.nextDouble();
		double y2 = input.nextDouble();

		Point2D p1 = new Point2D.Double(x1,y1);
		Point2D p2 = new Point2D.Double(x2, y2);

这样就解决了问题，TestPoint2D类就搞定了，以下是完整代码

import java.util.Scanner;
import java.awt.geom.Point2D;

public class TestPoint2D {
	public static void main(String[] args) {
		// Create a Scanner
		Scanner input = new Scanner(System.in);
		
		System.out.print("Enter point1's x-, y-coordinates:");
		double x1 = input.nextDouble();
		double y1 = input.nextDouble();
		System.out.print("Enter point2' s x-, y-coordinates:");
		double x2 = input.nextDouble();
		double y2 = input.nextDouble();

		Point2D p1 = new Point2D.Double(x1,y1);
		Point2D p2 = new Point2D.Double(x2, y2);
		System.out.println("p1 is " + p1.toString());
		System.out.println("p2 is " + p2.toString());
		System.out.println("The distance between pi and p2 is" + p1.distance(p1));
	}
}

运行结果如下

Enter point1’s x-, y-coordinates: 2.5 7
Enter point2’ s x-, y-coordinates:3.5 12
p1 is Point2D.Double[2.5, 7.0]
p2 is Point2D.Double[3.5, 12.0]
The distance between p1 and p2 is 5.0990195135927845

以上就是解决问题的全部过程，如果有幸被您看到，非常感谢指正（qiaoguangtong_1@126.com)

Thanks so much