How to refresh a JPanel?

Question

I am creating a small JPanel program to generate mazes. All of my code works but I want to display the maze generation in action. I edited my program to cause the paintComponent function to show the in progress maze. But I am in another class which is being passed my JPanel object so it can "refresh" the display.

What should I do that will call the paintComponent function to draw all the cells AND refresh the displays?

This is the configuration of the panel:

JPanel mainPanel = new JPanel();
mainPanel.setLayout(new BorderLayout());
gamePanel = new GamePanel();
controlPanel = new ControlPanel();
mainPanel.add(gamePanel, BorderLayout.CENTER);
mainPanel.add(controlPanel, BorderLayout.SOUTH);
mainPanel.revalidate();

This is the code expected to be called on repaint:

protected void paintComponent(Graphics pen){
      if(started){
          int count=0;
          for (MapCell c:coms){
              if (c.type!='w'){
                  count++;
              }
              c.paint(pen);
          }
          System.out.println("White space: " +count);
          System.out.println("Components: "+coms.size());
          for(Anno an:mapGen.ans){
              an.draw(pen,img,colWidth,rowHeight);
          }
      }

The print statements work fine after the maze generation but only the image "Anno" is drawn and it leaves a trail behind it. I have confirmed the list is getting correct data.

Answer 1

The cells now render correctly afterwards, but it still doesn't show during the algorithm.

Your calculation is probably blocking the event dispatch thread. Instead, iterate your algorithm in a background thread using SwingWorker, as shown here and here, and publish() interim results that process() can use to update your panel.