package demo; import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Point; import java.awt.geom.Path2D; import javax.swing.JFrame; import javax.swing.JPanel; public class PointTest extends JFrame{ int[] xPoints = { 71, 163, 163, 256}; int[] yPoints = { 89, 89, 254, 254}; // 创建多段线路径 Path2D path = new Path2D.Double(); Point point2 = new Point(117, 131); public PointTest() { path.moveTo(xPoints[0], yPoints[0]); for (int i = 1; i < xPoints.length; i++) { path.lineTo(xPoints[i], yPoints[i]); } System.out.println(path.contains(point2)); } public static void main(String[] args) { PointTest frame = new PointTest(); Canvas panel = new Canvas(); panel.path2d = frame.path; panel.point = frame.point; panel.point2 = frame.point2; frame.setContentPane(panel); frame.pack(); frame.setDefaultCloseOperation(3); frame.setLocationRelativeTo(null); frame.setVisible(true); } } class Canvas extends JPanel { Path2D path2d; Point point, point2; @Override public void paintComponent(Graphics g) { Graphics2D g2d = (Graphics2D) g; g2d.setColor(Color.BLUE); g2d.draw(path2d); g2d.setColor(Color.RED); g2d.fillOval(point.x, point.y, 4, 4); g2d.fillOval(point2.x, point2.y, 4, 4); } @Override public Dimension getPreferredSize() { return new Dimension(300, 200); } } 如何让point2只在线path上时候才为true

要确定`point2`只在线`path`上时才为`true`，可以使用`Path2D`的`contains()`方法来判断。但是在当前的代码中，`path`只是一条简单的多段线路径，并不包含闭合的区域。因此，我们可以使用`Path2D`的`contains()`方法来判断点是否在路径上。

以下是修改后的代码，其中添加了判断点是否在线上的逻辑：

package demo;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.geom.Path2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class PointTest extends JFrame{
    int[] xPoints = { 71, 163, 163, 256};
    int[] yPoints = { 89, 89, 254, 254};

    // 创建多段线路径
    Path2D path = new Path2D.Double();
    Point point2 = new Point(117, 131);

    public PointTest() {
        path.moveTo(xPoints[0], yPoints[0]);
        for (int i = 1; i < xPoints.length; i++) {
            path.lineTo(xPoints[i], yPoints[i]);
        }
        path.closePath();

        System.out.println(isPointOnPath(point2));
    }

    public boolean isPointOnPath(Point point) {
        return path.contains(point);
    }

    public static void main(String[] args) {
        PointTest frame = new PointTest();
        Canvas panel = new Canvas();
        panel.path2d = frame.path;
        panel.point = frame.point;
        panel.point2 = frame.point2;
        frame.setContentPane(panel);
        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

class Canvas extends JPanel {
    Path2D path2d;
    Point point, point2;

    @Override
    public void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.BLUE);
        g2d.draw(path2d);
        g2d.setColor(Color.RED);
        g2d.fillOval(point.x, point.y, 4, 4);
        g2d.fillOval(point2.x, point2.y, 4, 4);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(300, 200);
    }
}

在`PointTest`类中添加了一个`isPointOnPath()`方法，用于判断点是否在线上。在`PointTest`构造函数中，调用`isPointOnPath()`方法判断`point2`是否在线上，并输出结果。

这样修改后，当`point2`在线上时，输出为`true`，不在线上时，输出为`false`。