}
void registerDisplay(Display disp) {
display = disp;
}
void throwit() {
display.setForeground(Color.black);
int num = (int)(Math.random()*6 +1);
int i = counter++;
list.add(i, new Integer(num));
undo.add(i, new Memento(num));
display.setText(“”+num);
}
void previous() {
display.setForeground(Color.red);
btnDc.setEnabled(false);
if (undo.size() > 0) {
ct = undo.size()-1;
Memento num = (Memento)undo.get(ct);
display.setText(“”+num.getNumber());
undo.remove(ct);
}
if (undo.size() == 0)
display.setText(“0”);
}
void clear() {
list = new ArrayList();
undo = new ArrayList();
counter = 0;
display.setText(“0”);
btnDc.setEnabled(true);
}
}

MementoDemoDp.java

import java.awt.*;
import java.util.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.border.*;
import java.awt.FontMetrics;
class MementoDemoDp extends JFrame
implements ActionListener {
Mediator mediator = new Mediator();
MementoDemoDp() {
JPanel panel = new JPanel();
panel.add(new ButtonDice(this,mediator));
panel.add(new
ButtonPrevious(this,mediator));
panel.add(new ButtonClear(this,mediator));
JPanel dice = new JPanel();
Display disp = new Display(mediator);
dice.add(disp);
getContentPane().add(dice, “Center”);
getContentPane().add(panel, “South”);
setTitle(“Memento pattern example”);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setSize(400,200);
setVisible(true);
}
public void actionPerformed(ActionEvent ae) {
Command cmd = (Command)ae.getSource();
cmd.execute();
}
public static void main(String[] args) {
new MementoDemoDp();
}
}