修改JAVA程序，添加按钮

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Vector;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
@SuppressWarnings("serial")
public class SortGame extends JFrame implements ActionListener {
private JPanel mainPanel = new JPanel();
private JButton button[] = new JButton[16];
private int butNum[] = new int[16];
private Vector optionalNum = new Vector();
public SortGame(){
super("排块游戏");
mainPanel.setLayout(new GridLayout(4,4,3,3));
getContentPane().add(mainPanel);
for(int i=0; i<16; i++) {
button[i] = new JButton();
button[i].addActionListener(this);
mainPanel.add(button[i]);
butNum[i] = 0;
}
initButtonNum();
}
private void initButtonNum() {
for(int i=0; i<16; i++) {
optionalNum.add(String.valueOf(i));
}
int index = -1;
String str = null;
for(int i=0; i<16; i++){
index = (int)(Math.random()*optionalNum.size());
str = optionalNum.get(index);
if(str.equals("0")){
button[i].setText("");
butNum[i] = 0;
}
else {
button[i].setText(str);
butNum[i] = Integer.parseInt(str) ;
}
optionalNum.remove(index);
}
}
public void actionPerformed(ActionEvent e) {
int num =-1, location = -1;
int aim = -1;
int i=0;
if(e.getActionCommand().length() == 0)
return;
num = Integer.parseInt(e.getActionCommand());
while(i<16){
if(num == butNum[i++]){
location = i-1;
break;
}
}
int candidates[] = {location-1, location+1, location-4, location+4};
for(int j=0; j<4; j++){
if(check(candidates[j]))
aim = candidates[j];
}
if(aim >= 0 && aim < 16){
String tempStr = button[location].getText();
int tempNum = butNum[location];
button[location].setText("");
butNum[location] = 0;
button[aim].setText(tempStr);
butNum[aim] = tempNum;
}
if(evaluate()){
int choice = JOptionPane.showConfirmDialog(this, "你赢了！[请点击开始]再来一次.",null,JOptionPane.YES_OPTION);
if(choice == JOptionPane.YES_OPTION)
initButtonNum();
}
}
private boolean check(int index) {
if(index >= 0 && index < 15 && butNum[index] == 0)
return true;
else
return false;
}
private boolean evaluate() {
int i,j;
for(i=0; i<16; i++){
if(butNum[i] != i)
break;
}
if(i == 16) return true;

    for(i=0; i<15; i++){
        if(butNum[i] != i+1)
            break;
    }
    if(i == 15)  return true;
    
    for(i=0,j=15; j>=0; i++,j--){
        if(butNum[j] != i)
            break;
    }
    if(i == 16)  return true;
    
    for(i=0,j=15; j>0; i++,j--){
        if(butNum[j] != i+1)
            break;
    }
    if(i == 15)  return true;
    return false;
}
public static void main(String[] args) {
    SortGame game = new SortGame();
    game.setDefaultCloseOperation(EXIT_ON_CLOSE);
    game.setSize(400,400);
    game.setVisible(true);
}

}