这与我的上一个问题类似（请参见此处），但我仍然无法让一切正常工作。我现在可以显示实际的 GUI，但没有显示任何内容，例如我的按钮或您绘制的内容。如果有人可以提供帮助，将不胜感激！！谢谢！
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Paint{
public static void main(String[] args){
Win frame = new Win();
frame.setSize(500, 500);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
class gui extends JComponent{
Image image;
Graphics2D draw;
int x, y, prevX, prevY;
gui(){
setDoubleBuffered(false);
addMouseListener(new MouseAdapter(){
public void mousePressed(MouseEvent e){
prevX = e.getX();
prevY = e.getY();
}
});
addMouseMotionListener(new MouseMotionAdapter(){
public void mouseDragged(MouseEvent e){
x = e.getX();
y = e.getY();
draw.drawLine(prevX, prevY, x, y);
repaint();
prevX = x;
prevY = y;
}
});
}
public void changeColor(Color color)
{
draw.setPaint(color);
repaint();
}
public void clear(){
draw.setPaint(Color.white);
draw.fillRect(0, 0, getSize().width, getSize().height);
draw.setPaint(Color.black);
repaint();
}
public void paintComponent(Graphics g)
{
if(image == null)
{
image = createImage(getSize().width, getSize().height);
draw = (Graphics2D)image.getGraphics();
draw.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
clear();
}
g.drawImage(image, 0, 0, null);
}
}
class Win extends JFrame implements ActionListener{
JButton red, green, blue, clear;
gui gui = new gui();
Win(){
super("Paint");
setSize(500,500);
Container content=new Container();
content.setLayout(new BorderLayout());
content.add(gui, BorderLayout.CENTER);
content.setVisible(true);
JPanel panel = new JPanel();
content.add(panel, BorderLayout.SOUTH);
panel.setPreferredSize(new Dimension(32, 68));
panel.setMinimumSize(new Dimension(32, 68));
panel.setMaximumSize(new Dimension(32, 68));
red = new JButton("Red");
green = new JButton("Green");
blue = new JButton("Blue");
clear = new JButton("Clear");
red.setPreferredSize(new Dimension(50, 16));
green.setPreferredSize(new Dimension(50,16));
blue.setPreferredSize(new Dimension(50, 16));
panel.add(red);
panel.add(green);
panel.add(blue);
panel.add(clear);
panel.setVisible(true);
red.addActionListener(this);
green.addActionListener(this);
blue.addActionListener(this);
clear.addActionListener(this);
}
public void actionPerformed(ActionEvent e) {
if( e.getSource()==red){
gui.changeColor(Color.red);
repaint();
}
if( e.getSource()==green){
gui.changeColor(Color.green);
repaint();
}
if( e.getSource()==blue){
gui.changeColor(Color.blue);
repaint();
}
if( e.getSource()==clear){
gui.clear();
}
}
}