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1 import java.util.Observable;
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2 import java.util.Observer;
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3
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4 public class MessageBoard extends Observable {
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5 private String message;
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6
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7 public String getMessage() {
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8 return message;
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9 }
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10
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11 public void changeMessage(String message) {
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12 this.message = message;
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13 setChanged();
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14 notifyObservers(message);
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15 }
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16
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17 public static void main(String[] args) {
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18 MessageBoard board = new MessageBoard();
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19 Student bob = new Student();
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20 Student joe = new Student();
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21 board.addObserver(bob);
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22 board.addObserver(joe);
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23 board.changeMessage("More Homework!");
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24 }
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25 }
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26
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27 class Student implements Observer {
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28 public void update(Observable o, Object arg) {
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29 System.out.println("Message board changed: " + arg);
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30 }
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31 }
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