How to implement a swap function in a sliding tile puzzle?

Question

I am making a sliding tile puzzle. Below is my code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

public class GUI implements ActionListener{

private JFrame game;                    //Name the main window "game"
private JPanel borderPanel;             //Declare borderPanel for main window
private BorderLayout border;                //Name the borderPanel "border"
private ImageIcon[] image = new ImageIcon[12];      //Declare an array of images for tiles
private JButton[] tiles = new JButton[12];      //Declare an array for JButton inside the gridPanel
private JPanel gridPanel;               //Declare gridPanel
private GridLayout grid;                //Name the gridPanel "grid"
private int i;                      //Declare integer "i"

public GUI(){
    game = new JFrame();                    //Initial main window "game"
    game.setTitle("Puzzle");                //Change window title to "Puzzle"
    game.setSize(456, 392);                 //Set window size
    game.setResizable(false);               //fix the window's size
    game.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    borderPanel = new JPanel();     //Declare borderPanel
    border = new BorderLayout();        //Initial borderPanel
    borderPanel.setLayout(border);

    JButton newGameBtn = new JButton("New Game");       //Declare JButton "New Game"
    borderPanel.add (newGameBtn, BorderLayout.PAGE_START);  //Add a "new game" button on top
    newGameBtn.addActionListener(this);         //Add ActionListener function to JButton "newGamebtn"

    gridPanel = new JPanel();           //Declare gridPanel for the tiles
    GridLayout grid = new GridLayout(3, 4);     //Give the gridPanel 12boxes
    gridPanel.setLayout(grid);          //Initial gridPanel

    for (i = 0; i < 12; i++){
        image[i] = new ImageIcon("bart" + i + ".jpg");      //link the array and images together
        tiles[i] = new JButton(image[i]);           //Setup 12 JButtons and place images onto JButtons
        gridPanel.add(tiles[i]);                //Add the tiles to gridPanel
    }

    borderPanel.add (gridPanel, BorderLayout.CENTER);   //Put the gridPanel into the center of the borderPanel

    game.add(borderPanel);      //Add borderPanel to main frame
    game.setVisible(true);      //Make it visible
}

public void actionPerformed(ActionEvent click){

    Collections.shuffle(Arrays.asList(tiles));      //Shuffle the the array "tiles" in an arraylist
    shuffleTiles();                     //Function to re-layout all tiles
}

public void shuffleTiles(){
    gridPanel.removeAll();              //Remove all tiles in gridPanel
    for (JButton tilesorder : tiles){       //For each element name "tilesorder" in "tiles
        gridPanel.add(tilesorder);      //Add all tiles back onto gridPanel with new order
    }
    gridPanel.repaint();                //Clean the area after remove tiles in case of old images are still there
    gridPanel.revalidate();             //Re-layout the tiles
}

public static void main(String[] args){
    GUI game = new GUI();
}
}

I have declared 2 arrays, 1 for images and 1 for tiles. I shuffle the tiles with Collections.shuffle function. As of now, I can shuffle the tiles but I have no idea how to swap the tiles?

Any help will be appreciated. Thanks.