How to stop grid cell from redrawing in Java?

I am trying to generate a random color(between 4 colors) for each cell in a grid. I have managed to do so but it keeps redrawing itself over the outline of the grid and other elements of the grid. How can I make it so that the colors only draw once?, while my other elements keeps on drawing themselves? Here is the code I currently have:

import java.awt.*;
import java.util.Random;

public class Cell extends Rectangle {

private Random random;

public Cell(int x, int y) {

    super(x, y, 35, 35);
}


public void paint(Graphics g, Boolean highlighted) {

    int row;
    int col;

    for (row=0; row < 20 ; row++ ) {
        for (col =0; col <20 ; col++) {
            x=col * 35;
            y=row * 35;
            SurfaceType(g);
        }
    }


    g.setColor(Color.BLACK);
    g.drawRect(x, y, 35, 35);


    if (highlighted) {
        g.setColor(Color.LIGHT_GRAY);
        g.fillRect(x, y, 35, 35);
    } else {
        g.setColor(Color.DARK_GRAY);
        g.fillRect(x, y, 35, 35);
    }

}



@Override
public boolean contains(Point target){
    if (target == null)
        return false;
    return super.contains(target);
}

public void SurfaceType(Graphics g) {
   random= new Random();
   int randomNumber = random.nextInt( 5);

   switch (randomNumber) {
       case 1: // dirt
           g.setColor(new Color(102,51,0));
           g.fillRect(x,y,34,34);
           break;
       case 2: //grass
           g.setColor(new Color(102,153,0));
           g.fillRect(x,y,34,34);
           break;
       case 3: //tree
           g.setColor(new Color(0,102,0));
           g.fillRect(x,y,34,34);
           break;
       case 4: //rock
           g.setColor(new Color(182,182,182));
           g.fillRect(x,y,34,34);
           break;
   }



 }


}

This image shows what the grid looks like when I take out the code that randomizes the color out.

And this one shows with that part of code included: