Code:


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

public class fifteenGame extends JFrame
{
   
    private JFrame frame;
    String[] buttonNr = {"15","14","13","12","11","10","9","8","7","6","5","4","3","2","1",""};
   
    public fifteenGame()
    {
        makeFrame();
    }
   
    public void makeFrame(){
        frame = new JFrame();
        //this.setContentPane(frame);
        frame.setLayout(new GridLayout(4,4,3,3));
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.pack();
        fillButtons();
        frame.setBounds(100,100,300,200);
    }
   
    public static void main(String[] args){
       
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new fifteenGame();
            }
        });
    }
   
    public void fillButtons()
    {
        for(int i = 0; i < buttonNr.length;i++){
            Cell button = new Cell(""+ buttonNr[i]);
            frame.add(button,""+buttonNr[i]);
        }
           }


           public void keyPress(ActionEvent e){
        JButton b=(JButton)e.getSource();
        Component[] c = frame.getComponents();
        int labelPosition = getLabelNumber();
        int buttonPosition = getButtonNumber(b);
       

        if(buttonPosition+5 == labelPosition ||buttonPosition-5 == labelPosition || buttonPosition+1 == labelPosition || buttonPosition-1 == labelPosition){
            Component temp = frame.getComponent(labelPosition);
            frame.add(b,labelPosition);
            frame.add(temp,buttonPosition);
            this.validate();
           
        }
    }
   
    private int getButtonNumber(JButton button){
        Component[] c = frame.getComponents();
        for(int i=0;i<c.length;i++){
           
            if(c[i] instanceof Cell ){
                                if((Cell)c[i]==button){
                    return i;
                }
            }
        }
        return -1;
    }
   
    private int getLabelNumber(){
        Component[] c = frame.getComponents();
        for(int i=0;i<c.length;i++){
            if(c[i] instanceof JLabel){
                return i;
            }
        }
        return -1;
    }
   
    class Cell extends JButton implements ActionListener{   
       
   
       
        Cell(String name){
            this.setText(name);
            this.addActionListener(this);
           
        }
       
        public void actionPerformed(ActionEvent e) {
            keyPress(e);
        }
             
       
            }
        }