Putting images on random created buttons in Java

I am trying to create a game in Java. In the game, a player will encounter some obstacles by clicking on buttons. Up until now, those obstacles were defined as integers, and if a button was clicked, numbers that represented these objects appeared. I would like to change those numbers into images, but I can't change the count[random1][random2] from int to string. Do you have any suggestions? (I will only add the tree obstacle here and its relevant code).

public class Tiles implements ActionListener {
final static int TREES = 10; 
static JFrame frame = new JFrame("The Game");
JButton[] [] buttons = new JButton[5][5];
static int [] [] counts = new int [5] [5]; 
Panel grid = new Panel(); 

    public Tiles() {

    frame.setSize(400,400);
    frame.setLayout(new BorderLayout());


    makeGrid(); 

    frame.add(grid,  BorderLayout.CENTER);
    grid.setLayout(new GridLayout(5,5));
    for (int row = 0; row < buttons.length; row++) {
        for (int col = 0; col < buttons[0].length; col++) {
            buttons [row][col] = new JButton(); 
            buttons [row][col].addActionListener(this); 
            grid.add(buttons[row] [col]);
            buttons[row][col].setBackground(Color.WHITE);
        }

    }



    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    frame.setVisible(true);

}

public void makeGrid() {


        int numTrees = 2;  

        Random random = new Random(); 


        int i = 0;
        while (i < numTrees)  {
            int random1 = random.nextInt(5);
            int random2 = random.nextInt(5);
            if( counts [random1] [random2] == 0) {
                counts[random1] [random2] = TREES;
            i++; 
            }
        }
  }
  }