class NextPilot extends Pilot{
private String text;
public NextPilot(Mediator m, String s){
super( m );
text = s;
}
public void setText(String txt){
text = txt;
}
public String getSelection(){
return( text );
}
public void Show(){
System.out.println(“NextPilot = “ + text);
}
}

III. Memento

The memento design pattern is that pattern in which one object stores the previous state (undo via rollback) of another object. This pattern operates on a single object. The objects originator and the caretaker use this design pattern. The object originator maintains the original state while the object caretaker assist to the originator. First the caretaker object asked to the originator for the memento object then it does the operation (or sequence of operations) it is going to do. It returns the memento object to the originator to roll back the state before the operations. Be careful while using this pattern, as the originator may change other objects or resources. To develop a memento featured program we need to combine the design patterns like Iterator, Mediator or Command. Here we are taking an example that uses the Mediator design pattern. To demonstrate the concept of Memento design pattern we are taking an example of dice that records the dice numbers.

Command.java

import java.awt.*;
import java.util.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.border.*;
import java.awt.FontMetrics;
interface Command {
void execute();
}
Memento.java
class Memento {
int number;
Memento(int num) {
number = num;
}
int getNumber() {
return number;
}
}

ButtonDice.java

import java.awt.*;
import java.util.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.border.*;
import java.awt.FontMetrics;
class ButtonDice extends JButton implements
Command {
Mediator mediator;
ButtonDice(ActionListener al, Mediator med) {
super(“Throw Dice”);
addActionListener(al);
mediator = med;
mediator.registerDice(this);
}
public void execute() {
mediator.throwit();
}
}