Замена местами кнопок в ArrayList JavaSwing

public void actionPerformed(ActionEvent e) {
        event = (JButton) e.getSource();
        System.out.println(event.equals(button1));
        if (event.equals(button1)) {
            int x = button.indexOf(button1);
            int y = button.indexOf(button0);  //меняю в ArrayList. местами кнопки
            button.set(x, button0);
            button.set(y, button1);
            x = button.indexOf(button1);
            y = button.indexOf(button0);
        }
 
    }

package barley_break_GUI;
 
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
 
public class Barley_Break_GUI_Start extends JPanel implements
        Barley_Break_Constance {
 
    static Barley_Break_GUI_Start start = new Barley_Break_GUI_Start();
    JFrame frame = new JFrame();
    ArrayList<JButton> button = new ArrayList<JButton>(16);
    JPanel panelbutton = new JPanel();
    int width = 0;
    int height = 0;
 
 public Barley_Break_GUI_Start() {
        Barley_Break_GUI_Engine engine = new Barley_Break_GUI_Engine(start,
                button);
        ActionListener action = new Barley_Break_GUI_Engine(start, button);
        button1.addActionListener(action);
    }
public static void main(String[] args) {
        start.createFrame();
 
    }
 
    public void createFrame() {
        start.createDimension();
        frame.setSize(width, height);
        frame.setTitle("Barley_Break");
        Image image = new ImageIcon("icon.gif").getImage();
        frame.setIconImage(image);
        start.createan();
        frame.getContentPane().add(panelbutton, BorderLayout.CENTER);
        frame.setLocationByPlatform(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
 
    }
 
    public void createDimension() {
        Toolkit kit = Toolkit.getDefaultToolkit();
        Dimension dim = kit.getScreenSize();
        width = dim.width / 4;
        height = dim.height / 4;
    }
 public void createan() {
        button.add(button0);
        button.get(0).setEnabled(false);
        button.add(button1);
        button.add(button2);
        button.add(button3);
        button.add(button4);
        button.add(button5);
        button.add(button6);
        button.add(button7);
        button.add(button8);
        button.add(button9);
        button.add(button10);
        button.add(button11);
        button.add(button12);
        button.add(button13);
        button.add(button14);
        button.add(button15);
        panelbutton.setLayout(new GridLayout(4, 4));
        for (int i = 0; i < button.size(); i++) {
            panelbutton.add(button.get(i));
        }
 
    }
 }
                                          
package barley_break_GUI;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import javax.swing.JButton;
public class Barley_Break_GUI_Engine implements Barley_Break_Constance,
        ActionListener {
    Barley_Break_GUI_Start start;
    ArrayList<JButton> button;
    JButton event;
 
    public Barley_Break_GUI_Engine(Barley_Break_GUI_Start start,
            ArrayList<JButton> button) {
        this.start = start;
        this.button = button;
    }
 
    @Override
    public void actionPerformed(ActionEvent e) {
        event = (JButton) e.getSource();
        System.out.println(event.equals(button1));
        if (event.equals(button1)) {
            int x = button.indexOf(button1);
            int y = button.indexOf(button0);
            button.set(x, button0);
            button.set(y, button1);
            x = button.indexOf(button1);
            y = button.indexOf(button0);
        }
 
    }
 
}
 
package barley_break_GUI;
import javax.swing.JButton;
public interface Barley_Break_Constance {
    JButton button0 = new JButton(" ");
    JButton button1 = new JButton("1");
    JButton button2 = new JButton("2");
    JButton button3 = new JButton("3");
    JButton button4 = new JButton("4");
    JButton button5 = new JButton("5");
    JButton button6 = new JButton("6");
    JButton button7 = new JButton("7");
    JButton button8 = new JButton("8");
    JButton button9 = new JButton("9");
    JButton button10 = new JButton("10");
    JButton button11 = new JButton("11");
    JButton button12 = new JButton("12");
    JButton button13 = new JButton("13");
    JButton button14 = new JButton("14");
    JButton button15 = new JButton("15");
}