无法访问JPanel的公共方法/变量，并且无法从Jpanel访问其他公共方法/变量

Question

package client;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.ImageIcon;
import javax.swing.JPanel;
import javax.swing.JTextArea;

public class YootPanel extends JPanel
{

    private ImageIcon bgIcon;
    public JTextArea textBox;
    public ClientUI clientUI;
    public static final int HORSE_HEIGHT = 25;
    public static final int HORSE_WIDTH = 40;
    public int r1,r2,r3,r4;
    public int b1,b2,b3,b4;
    YootPanelPlot plot;

    public YootPanel(ClientUI clientUI)
    {
        super();    
        init_rest();
        init_bg();
            plot =  = new YootPanelPlot();
        this.setVisible(true);
        this.clientUI = clientUI;
    }

    private void init_bg()
    {
        java.net.URL imgUrl = ClientUI.class.getResource("../images/images/background.png");
        bgIcon = new ImageIcon(imgUrl);
    }

    protected void paintComponent(Graphics g)
    {
        try
        {
            g.drawImage(bgIcon.getImage(), -20, 0, null);
            super.paintComponent(g);
        } catch (Exception e)
        {


        set_Loc();


        g.setColor(Color.RED);
        g.fillOval(plot.plot[0][r1], plot.plot[1][r1], HORSE_WIDTH, HORSE_HEIGHT);
        g.fillOval(plot.plot[0][r2], plot.plot[1][r2], HORSE_WIDTH, HORSE_HEIGHT);
        g.fillOval(plot.plot[0][r3], plot.plot[1][r3], HORSE_WIDTH, HORSE_HEIGHT);
        g.fillOval(plot.plot[0][r4], plot.plot[1][r4], HORSE_WIDTH, HORSE_HEIGHT);
        g.setColor(Color.BLUE);
        g.fillOval(plot.plot[0][b1], plot.plot[1][b1], HORSE_WIDTH, HORSE_HEIGHT);
        g.fillOval(plot.plot[0][b2], plot.plot[1][b2], HORSE_WIDTH, HORSE_HEIGHT);
        g.fillOval(plot.plot[0][b3], plot.plot[1][b3], HORSE_WIDTH, HORSE_HEIGHT);
        g.fillOval(plot.plot[0][b4], plot.plot[1][b4], HORSE_WIDTH, HORSE_HEIGHT);
        System.err.println("Paint");
        }
    }

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

    }

private void init_rest()
{
        this.setBorder(javax.swing.BorderFactory.createTitledBorder("Yoot Map"));
        this.setFocusable(false);
        this.setMinimumSize(new java.awt.Dimension(670, 400));
        this.setName("map"); // NOI18N
        this.setOpaque(false);
        this.setPreferredSize(new java.awt.Dimension(630, 400));
        this.setSize(new java.awt.Dimension(630, 400));
        this.setVerifyInputWhenFocusTarget(false);

        org.jdesktop.layout.GroupLayout yootMapLayout = new org.jdesktop.layout.GroupLayout(this);
        this.setLayout(yootMapLayout);
        yootMapLayout.setHorizontalGroup(
        yootMapLayout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING).add(0, 658, Short.MAX_VALUE));
yootMapLayout.setVerticalGroup(
        yootMapLayout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING).add(0, 442, Short.MAX_VALUE));
}

    public void set_Loc()
    {
        try
        {
            System.err.println("......"+clientUI.client.c2.blueHorseLocation[0]);
            r1 = clientUI.client.c2.getRed(0);
            r2 = clientUI.client.c2.getRed(1);
            r3 = clientUI.client.c2.getRed(2);
            r4 = clientUI.client.c2.getRed(3);
            b1 = clientUI.client.c2.blueHorseLocation[0];
            b2 = clientUI.client.c2.blueHorseLocation[1];
            b3 = clientUI.client.c2.blueHorseLocation[2];
            b4 = clientUI.client.c2.blueHorseLocation[3];
        } catch (NullPointerException e)
        {
             e.printStackTrace();
        }
    }
}

我想做的是获取在哪里绘制椭圆的更新。 然而最后一部分的 r1 = clientUI.client.c2.getRed(1);抛出 NullPointerException

所以我尝试访问这个类公共变量 r1，r2 ...等但是，我也无法访问这些公共变量......

有没有办法可以修改这些变量，以便我可以移动椭圆形当我得到新的坐标更新时？

Answer 1

不要使用公共变量。

定义方法来更新您想要更改的任何属性的值。

此外，自定义绘画是通过重写paintComponent()方法来完成的。您不应该重写 Paint() 方法。

Answer 2

好吧，我很愚蠢，在创建对象时做了错误的工作......
我应该用的

YootPanel object = new YootPanel();

，但我

JPanel object = new YootPanel();

却用了......
难怪我无法访问我在 YootPanel 类中创建的方法......

谢谢大家的回答！