I’ve been trying to find a workarounds, but have not found one,

especially for the getGraphics() method: how else can the graphics be

added to the panel?

你记得需要绘制一个变量,并在paintComponent()中使用它.

例如,你似乎在尝试在你的另一个问题上看起来像：

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class PaintRectangle extends JPanel {

private Point mouseLocation;

public PaintRectangle() {

setPreferredSize(new Dimension(500, 500));

MouseAdapter listener = new MouseAdapter() {

@Override

public void mousePressed(MouseEvent e) {

updateMouseRectangle(e);

}

private void updateMouseRectangle(MouseEvent e) {

mouseLocation = e.getPoint();

repaint();

}

@Override

public void mouseDragged(MouseEvent e) {

updateMouseRectangle(e);

}

@Override

public void mouseReleased(MouseEvent e) {

mouseLocation = null;

repaint();

}

};

addMouseListener(listener);

addMouseMotionListener(listener);

}

private Rectangle getRectangle() {

if(mouseLocation != null) {

return new Rectangle(mouseLocation.x - 5, mouseLocation.y - 5, 10, 10);

}

else {

return null;

}

}

@Override

protected void paintComponent(Graphics g) {

super.paintComponent(g);

Rectangle rectangle = getRectangle();

if(rectangle != null) {

Graphics2D gg = (Graphics2D) g;

gg.setColor(Color.BLUE);

gg.fill(rectangle);

gg.setColor(Color.BLACK);

gg.draw(rectangle);

}

}

public static void main(String[] args) {

EventQueue.invokeLater(new Runnable() {

@Override

public void run() {

JFrame frame = new JFrame("Test");

frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

frame.getContentPane().add(new PaintRectangle());

frame.pack();

frame.setLocationRelativeTo(null);

frame.setVisible(true);

}

});

}

}