如果通过递归函数调用paintComponent不起作用？

Question

1. 我希望看到所有的Points一个接一个,但我看到只能看到1分.看到所有的变化,我改变了Points什么？
2. 在System.out你可以看到10次"设置"然后2次"paintComponent".在调用每个时间集之后我应该改变什么呢？它改变了"paintComponente"？

================================================== ================================

public class exampe extends JPanel  
{
    int x; 
    int y;

    public void paintComponent(Graphics g) 
    {
        super.paintComponent(g);

        Graphics2D g2 = (Graphics2D) g;
        g2.fillOval(x-2,y-2,4,4);
        System.out.println("paintComponent");        
    }

    public void set(int X, int Y)
    {
        x = X;
        y = Y;
        System.out.println("set");
        super.repaint();
    }

    public static void main(String args[]) 
    {   
        int e=1;

        JFrame frame = new JFrame("TEST");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        exampe ex= new exampe();
        JScrollPane scroll = new JScrollPane(ex);
        frame.getContentPane().add(scroll);

        frame.setSize(400, 300);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);

        for(int i=0; i< 10; ++i)
            ex.set(e+i,e+i);         
    }
}

Answer 1

*简单说明为什么你只能看到最后的更新:*

引自Chet Haase和Romain Guy的肮脏富客户的报价

It is important to note that repaint requests get “coalesced,” or combined. 
So, for example, if you request a repaint and there is already one on the 
queue that has not yet been serviced, then the second request is ignored 
because your request for a repaint will already be ful?lled by the earlier 
request. This behavior is particularly helpful in situations where many
repaint requests are being generated, perhaps by very different situations 
and components, and Swing should avoid processing redundant requests and 
wasting effort.

试试这个,问一下你不清楚的事情:

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class PointsExample
{   
    private CustomPanel contentPane;
    private Timer timer;
    private int x = 1;
    private int y = 1;
    private ActionListener timerAction = new ActionListener()
    {   
        public void actionPerformed(ActionEvent ae)
        {
            contentPane.set(x, y);
            x++;
            y++;
            if (x == 450)
                timer.stop();
        }
    };
    /*
     * This is just JFrame, that we be 
     * using as the Base for our Application.
     * Though here we are calling our
     * JPanel (CustomPanel), whose
     * paintComponent(...) method, we had
     * override.
     */
    private void createAndDisplayGUI()
    {
        JFrame frame = new JFrame("Locate Mouse Position");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        contentPane = new CustomPanel();
        frame.setContentPane(contentPane);  
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
        timer = new Timer(100, timerAction);
        timer.start();
    }

    public static void main(String\u005B\u005D args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new PointsExample().createAndDisplayGUI();
            }
        });
    }
}

class CustomPanel extends JComponent
{
    private int x;
    private int y;

    public void set(int a, int b)
    {
        x = a;
        y = b;
        repaint();
    }   

    @Override
    public Dimension getPreferredSize()
    {
        return (new Dimension(500, 500));
    }

    @Override
    public void paintComponent(Graphics g)
    { 
        g.clearRect(0, 0, getWidth(), getHeight());
        Graphics2D g2 =(Graphics2D) g;
        g2.fillOval(x, y, 4, 4);        
    }
}

下面是代码,它允许您在for循环中迭代时查看您的点,尽管这种方法非常不鼓励,因为许多与之相关的缺点.虽然尝试一下这个而不是repaint()调用paintImmediately(int ...)或paintImmediately(Rectangle rect)

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class PointsExample
{   
    private CustomPanel contentPane;
    private Timer timer;
    private int x = 1;
    private int y = 1;

    /*
     * This is just JFrame, that we be 
     * using as the Base for our Application.
     * Though here we are calling our
     * JPanel (CustomPanel), whose
     * paintComponent(...) method, we had
     * override.
     */
    private void createAndDisplayGUI()
    {
        JFrame frame = new JFrame("Locate Mouse Position");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        contentPane = new CustomPanel();
        frame.setContentPane(contentPane);  
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);

        for (int i = 0; i < 500; i++)
        {
            contentPane.set(x, y);
            x++;
            y++;
            if (x == 450)
                break;
        }
    }

    public static void main(String\u005B\u005D args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new PointsExample().createAndDisplayGUI();
            }
        });
    }
}

class CustomPanel extends JComponent
{
    private int x;
    private int y;

    public void set(int a, int b)
    {
        x = a;
        y = b;
        paintImmediately(0, 0, getWidth(), getHeight());

    }   

    @Override
    public Dimension getPreferredSize()
    {
        return (new Dimension(500, 500));
    }

    @Override
    public void paintComponent(Graphics g)
    { 
        super.paintComponent(g);
        g.fillOval(x, y, 4, 4);         
    }
}