$//$ fill out the code

$//$observer$.$java

package question$1$;

public interface Observer $\{$

void valueHasChanged$($T newValue$)$;

$\}$

$//$statevariable$.$java

package question$1$;

$//$ Create an observer that can alert an observer of a value changed

public class StateVariable $\{$

public StateVariable$($Observer observer$)\{$

$\}$

public void setValue$($T newValue$)\{$

$\}$

$\}$

$//$question$1.$java

package question$1$;

import org.junit.Assert;

import org.testng.annotations.Test;

class Watcher implements Observer$\{$

int count;

T lastValueSeen;

@Override

public void valueHasChanged$($T newValue$)\{$

count$++$;

lastValueSeen $=$ newValue;

$\}$

$\}$

public class Question$1\{$

$/*$

$*$ Create an observer that alerts when a value has changed

$*/$

@Test

public void test$()\{$

var watcher $=$ new Watcher$()$;

StateVariable intState $=$ new StateVariable$<>($watcher$)$;

intState.setValue$(1)$;

Assert.assertEquals$($watcher$.$count, $1)$;

Assert.assertEquals$(($int$)$watcher$.$lastValueSeen, $1)$;

intState.setValue$(2)$;

Assert.assertEquals$($watcher$.$count, $2)$;

Assert.assertEquals$(($int$)$watcher$.$lastValueSeen, $2)$;

$\}$

$\}$