Tilemap drawing not working Java

Question

I am making a small program that just draws a tilemap on my JPanel, but when i run the program, it draws the map, but its draws it twice, and when i maximize the window everything disappears.

here is my code:

 package main;

  import javax.swing.*;

  import java.awt.*;
  import java.io.*;
  import java.util.*;

  public class Board extends JPanel{

    int width = 10;
   int height = 10;
    int size = 30;

   int x;
   int y;

   int[][] map = map1.map;
   ArrayList<Tile> tiles = new ArrayList<Tile>();

   public Board(){

    loadMap();

    Thread t = new Thread(){

        public void run(){

            while(1 != 0){
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                repaint();

            }

        }

    };

    t.start();

    }

   public void loadMap(){
    int x = 0;
    int y = 0;

    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {

            int tex = map[i][j];
            Tile t = new Tile(x,y,tex);         
            tiles.add(t);

            x+= size;
        }
        y += size;
    }
    }

   public void drawMap(Graphics g){

   int index = 0;

    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {

            Tile t = tiles.get(index);

            if(t.tex == 0)
                g.setColor(Color.gray);
            else if(t.tex == 1)
                g.setColor(Color.magenta);

            g.fillRect(x,y,size,size);

            index++;
            x += size;
        }
        x = 0;
        y += size;
    }

   }

   public void paint(Graphics g){

    drawMap(g);
   }








    public static void main(String[] args){

        JFrame j = new JFrame();
        j.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        j.setVisible(true);
        j.add(new Board());
        j.setSize(600,600);
        j.setLocationRelativeTo(null);

    }



 }

My tile class and map class are self explanatory, the Tile class just holds a couple variables x,y, and the map just has an array[][] in it, and those don't seem to be the problem.

It prints the map out the way i wanted it to but then it has a clone below it and when i resize the window it everything just disappears. I don't know why it is doing this, and any help would be appreciated.

Thanks

Answer 1

Without having run the code:

1.

You are breaking the paint chain. But not calling super.paint you are not allowing the component to prepare itself properly for painting. Painting is a complex series of chained method calls which work together to produce the desired output, unless you're prepared to take over this work, you must always call super.xxx first.

It is typically recommended that you override paintComponent instead, for a vertiy of reasons, one of which you've just discovered...

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    drawMap(g);
}

See Painting in AWT and Swing and Performing Custom Painting for more details about how painting in Swing works...

2.

Your drawMap method is relying on instance fields to draw the grid, this means that each time the method is called, the values of y (in particular) are the same as they were when the method last exited...

No there's no real reason that they should be instance fields, they only have context within the drawMap method...

public void drawMap(Graphics g) {

    int x = 0;
    int y = 0;
    
    int index = 0;

    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {

            Tile t = tiles.get(index);

            if (t.tex == 0) {
                g.setColor(Color.gray);
            } else if (t.tex == 1) {
                g.setColor(Color.magenta);
            }

            g.fillRect(x, y, size, size);

            index++;
            x += size;
        }
        x = 0;
        y += size;
    }

}