Question

尝试执行鼠标事件分配。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，它应该创建一个小的橙色点，向下5个像素，右边5个像素。该分配需要三个程序，Dots，DotsPanel和DrawDots。该程序还应该有一个总点数的计数器。现在程序编译，但程序完全中断，并在我尝试运行它时给了我很多错误。我现在有点迷失，因为我是这个GUI和用户mouseEvents的新手。谢谢！我特别难以解决如何将Dots类作为Point进行投射。

以下是说明的副本：

修改“Dots”示例。包含一个Dots类，其中包含一个构造函数，用于初始化点的颜色和点位置。 Dots类还应包括两个访问器方法。 ArrayList现在将包含要绘制的点而不是点的列表。按下鼠标时，程序会绘制一个绿色圆圈（如原始设计中所示）。当鼠标被释放时，程序会绘制一个黄色圆圈，向右翻译5个像素，从释放位置向下翻译5个像素。务必跟踪总点数。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，您应该使用Iterator<Dots> pointIterator = pointList.iterator();。这有助于编译器在uncastable类型的情况下发出警告（这是你得到的第一个错误）。在paintComponent方法中，您应该稍后使用Point drawPoint = pointIterator.next().getPointP();和Point drawPoint2 = pointIterator.next().getPointP();视图行。

在修改之后，程序会运行（至少在我的机器上）。< / p>

无法创建点绘图程序并投射

1 个答案: