Java – the contents of the window disappear when minimized

I have a simple class that draws a line when the mouse is dragged or a point when the mouse is pressed (released)

When I minimize the application and restore it, the contents of the window disappear, except for the last point (pixel) I know the method super Paint (g) redraws the background every time the window changes, but the result seems to be the same whether I use it or not The difference between them is that when I don't use it, I draw more than one pixel on the window, not all my paintings How can I solve this problem?

This is the class

package painting;

import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import javax.swing.JFrame;
import javax.swing.JPanel;

class CustomCanvas extends Canvas{   
    Point oldLocation= new Point(10,10);
    Point location= new Point(10,10);
    Dimension dimension = new Dimension(2,2);     
    CustomCanvas(Dimension dimension){  
        this.dimension = dimension;   
        this.init();
        addListeners();
    }    
    private void init(){                     
        oldLocation= new Point(0,0);
        location= new Point(0,0);
    }
    public void paintLine(){
        if ((location.x!=oldLocation.x) || (location.y!=oldLocation.y)) {         
            repaint(location.x,location.y,1,1);                                   
        } 
    }
    private void addListeners(){
        addMouseListener(new MouseAdapter(){
            @Override
            public void mousePressed(MouseEvent me){                   
                oldLocation = location;
                location = new Point(me.getX(),me.getY());
                paintLine();
            }
            @Override
            public void mouseReleased(MouseEvent me){                
                oldLocation = location;
                location = new Point(me.getX(),me.getY());
                paintLine();
            }
        });
        addMouseMotionListener(new MouseMotionAdapter() {
            @Override
            public void mouseDragged(MouseEvent me){                
                oldLocation = location;
                location = new Point(me.getX(),me.getY());
                paintLine();
            }
        });
    }
    @Override
    public void paint(Graphics g){  
        super.paint(g);
        g.setColor(Color.red);       
        g.drawLine(location.x,oldLocation.x,oldLocation.y);                
    }
    @Override
    public Dimension getMinimumSize() {
        return dimension; 
    }
    @Override
    public Dimension getPreferredSize() {
        return dimension;
    }

}
class CustomFrame extends JPanel {
    JPanel displayPanel = new JPanel(new BorderLayout());
    CustomCanvas canvas = new CustomCanvas(new Dimension(200,200));        
    public CustomFrame(String titlu) {            
        canvas.setBackground(Color.white);
        displayPanel.add(canvas,BorderLayout.CENTER);            
        this.add(displayPanel);
    }   
}
public class CustomCanvasFrame {
    public static void main(String args[]) {
        CustomFrame panel = new CustomFrame("Test Paint");
        JFrame f = new JFrame();
        f.add(panel);
        f.pack();
        SwingConsole.run(f,700,700);
    }
}

Solution

You have not stored the state of the point you are drawing When a panel is redrawn, it displays only information about the last point it was drawn

Reply to comments:

You need to have a points set, such as ArrayList < point > location = new ArrayList < point > ();

Then, in your listener: location add(new Point(me.getX(),me. getY()));

Finally, in paintline():

for (Point location : locations) {
  repaint(location.x,1); 
}

Collection locations are often referred to as display lists Most graphics programs use them

Reply to comments:

Yes, I hope so I just throw an idea according to your code to give you a starting point It's almost certainly a bad idea to do exactly what I describe