在创建点绘图程序和铸造时遇到麻烦

Question

尝试分配鼠标事件。这个想法是，当用户点击鼠标时，程序绘制一个小绿点，当鼠标被释放时，它应该创建一个小橙色点，向下5像素，右边5像素。作业需要三个程序，Dots, DotsPanel和DrawDots。该程序还应该有一个总点数计数器。现在程序可以编译了，但是程序完全崩溃了，当我试图运行它时，它给了我大量的错误。我现在有点迷路了，因为我是这个GUI和用户mouseEvents的新手。谢谢你！我特别遇到了如何将Dots类转换为Point的麻烦。

这是说明书的副本:

修改"Dots"示例。包括一个Dots类，该类包含一个构造函数，用于初始化圆点的颜色和点位置。Dots类还应该包括两个访问器方法。ArrayList现在将包含一个要绘制的点的列表，而不是点。当按下鼠标时，程序绘制一个绿色的圆圈(与原始设计一样)。当鼠标被释放时，程序绘制一个黄色圆圈，从释放位置向右平移5像素，向下平移5像素。一定要记录点的总数。你应该有三个文件:Dots, DotsPanel, DrawDots。(10分)

/**
 * @(#)Dots.java
 *
 *
 * @author
 * @version 1.00 2015/5/16
 */
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

public class Dots
{
    Point p;
    Color col;
    public Dots(Color c, Point x)
    {
        p=x;
        col=c;
    }

    public Point getPointP()
    {
        return p.getLocation();
    }
    public Color getPointC()
    {
        return col;
    }
}

…

//represents the primary panel for the Dots program on which the
//dots are drawn
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
public class DotsPanel extends JPanel
{
    private final int WIDTH = 300, HEIGHT = 300;
    private final int RADIUS = 6;
    private ArrayList<Dots> pointList;
    private int count;
    //Sets up this panel to listen for mouse events.
    public DotsPanel()
    {
        pointList = new ArrayList<Dots>();
        count = 0;
        addMouseListener(new DotsListener());
        setBackground(Color.black);
        setPreferredSize(new Dimension(WIDTH, HEIGHT));
    }
    //Draws all of the dots stored in the list
    public void paintComponent(Graphics page)
    {
        super.paintComponent(page);

        //Retrieve an iterator for the ArrayList of points
        Iterator pointIterator = pointList.iterator();
        while(pointIterator.hasNext())
        {
            page.setColor(Color.green);
            Point drawPoint = (Point) pointIterator.next();
            page.fillOval(drawPoint.x - RADIUS, drawPoint.y - RADIUS,
                            RADIUS * 2, RADIUS * 2);

            page.setColor(Color.yellow);
            Point drawPoint2 = (Point) pointIterator.next();
            page.fillOval(drawPoint2.x - RADIUS+5, drawPoint2.y - RADIUS+5,
                            RADIUS * 2, RADIUS * 2);
        }
        page.drawString("Count: " + count, 5, 15);
    }
    //represents the lister for mouse events
    private class DotsListener implements MouseListener
    {
        //Adds the current point to the list of points and redraws
        //whenever the mouse button is pressed
        public void mousePressed(MouseEvent event)
        {
            Dots dot1 = new Dots(Color.GREEN, event.getPoint());
            pointList.add(dot1);
            count++;
            repaint();
        }
        public void mouseReleased(MouseEvent event)
        {
            Dots dot2 = new Dots(Color.YELLOW, event.getPoint());
            pointList.add(dot2);
            count++;
            repaint();
        }
        //Provide empty definitions for unused event methods
        public void mouseClicked(MouseEvent event) {}
        public void mouseEntered(MouseEvent event) {}
        public void mouseExited(MouseEvent event) {}
    }
}

…

//demonstrates mouse events and drawing on a panel
import javax.swing.*;
public class DrawDots
{
    //Creates and displays the application frame
    public static void main(String[] args)
    {
        JFrame dotsFrame = new JFrame("Dots");
        dotsFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        dotsFrame.getContentPane().add(new DotsPanel());
        dotsFrame.pack();
        dotsFrame.setVisible(true);
    }

}

Answer 1

首先应该使用Iterator<Dots> pointIterator = pointList.iterator();。这有助于编译器在不可浇注类型的情况下警告您(这是您得到的第一个错误)。在paintComponent方法中，您应该稍后使用Point drawPoint = pointIterator.next().getPointP();和Point drawPoint2 = pointIterator.next().getPointP();视图线。

修改后程序运行(至少在我的机器上)