Question

我是java Swing的初学者。我的代码是这样的：

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;

public class LineDrawing extends JComponent
{   
    public static void main(String[] args)
    {
        JFrame frame = new JFrame();
        JPanel panel = new JPanel();

        int startX = 0;
        int startY = 0;
        int endX = 0;
        int endY = 0;

        addMouseListener(new MouseListener(){
            @Override
            public void mousePressed(MouseEvent e)
            {
                startX = e.getXOnScreen();
                startY = e.getYOnScreen();
            }

            @Override
            public void mouseReleased(MouseEvent e)
            {
                endX = e.getXOnScreen();
                endY = e.getYOnScreen();
                Draw d = new Draw();
                d.lineDraw(startX,startY,endX,endY);
                panel.add(d);
                frame.add(panel);
            }

            @Override
            public void mouseClicked(MouseEvent e){}

            @Override
            public void mouseEntered(MouseEvent e){}

            @Override
            public void mouseExited(MouseEvent e){}
        });

        addMouseMotionListener(new MouseMotionListener(){
            @Override
            public void mouseDragged(MouseEvent e)
            {
                endX = e.getXOnScreen();
                endY = e.getYOnScreen();
            }

            @Override
            public void mouseMoved(MouseEvent e){}
        });

        frame.setSize(500,400);
        frame.setResizable(false);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    public class Draw extends JPanel
    {
        public void lineDraw(int x1,int y1,int x2,int y2)
        {
            @Override
            protected void paintComponent(Graphics g)
            {
                super.paintComponent(g);
                g.setColor(Color.black);
                g.drawLine(x1,y1,x2,y2);
            }
        }
     }
}

当我执行此操作时，它给了我这个错误：

如何增强此代码并解决上述错误。

我也见过其他代码，但paintComponent中出现了错误。

如果我在paintComponent之前放置@Override ...它会出现此错误：

1）';'声明遗失。 2）非法开始表达。

Answer 1

与BackSlash评论一样，您无法在现有内容中声明方法。

试试这个：

public class Draw extends JPanel {

    private int[] line = new int[4];

    public void lineDraw(int x1,int y1,int x2,int y2) {
        line[0] = x1;
        line[1] = y1;
        line[2] = x2;
        line[3] = y2;
        repaint();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.black);
        g.drawLine(line[0],line[1],line[2],line[3]);
    }  
}

要绘制多行，您需要将行数组添加到另一个数据结构（如ArrayList）中，并在paintComponent方法中迭代此列表并绘制所有内容。

public void paintComponent（Graphics g）无法正常工作

1 个答案: