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tnelsontnelson
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add: sep 16 exercise
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‎F25/.gitignore‎

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node_modules
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.DS_Store

‎F25/sep16_refinements/exercise/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>org.example</groupId>
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<artifactId>queue_manager_2</artifactId>
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<version>1.0-SNAPSHOT</version>
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<properties>
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<maven.compiler.source>18</maven.compiler.source>
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<maven.compiler.target>18</maven.compiler.target>
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</properties>
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</project>

‎F25/sep16_refinements/exercise/src/main/java/edu/brown/cs32/livecode/dispatcher/HoursDispatcher.java‎

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package edu.brown.cs32.livecode.dispatcher;
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import edu.brown.cs32.livecode.dispatcher.utils.TABusyException;
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import edu.brown.cs32.livecode.dispatcher.utils.Utils;
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import edu.brown.cs32.livecode.records.Student;
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import edu.brown.cs32.livecode.records.TA;
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import java.util.*;
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/**
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* A (very incomplete) dispatcher class for TA hours.
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*/
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public class HoursDispatcher {
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/** Single queue that the dispatcher will get students from */
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private final Deque<Student> queue;
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/** TAs on duty */
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private final Map<TA, Integer> minutesLeft = new HashMap<>();
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/** How many students have been helped by *any* dispatcher instance. */
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static int studentsHelped = 0;
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/**
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* @param signups an Iterator that provides Student objects
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*/
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HoursDispatcher(Deque<Student> signups) {
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this.queue = signups;
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}
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/**
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* Add an on-duty TA
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* @param ta the TA who is arriving for hours
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* @param minutes the number of minutes that this TA will stay
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*/
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void addTA(TA ta, int minutes) {
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minutesLeft.put(ta, minutes);
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}
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/**
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* Running this method starts the dispatcher.
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*/
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public void dispatch() {
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System.out.println(Utils.timestamp()+
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" Dispatcher: Welcome to edu.brown.cs32.livecode hours!");
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// Loop forever: new students may arrive over time
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while(true) {
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// Is there a student waiting right now?
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if(queue.peek() != null) {
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// Who will help this student?
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// TODO: later, prioritize free TAs with a specialty matching the student's question.
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Optional<TA> maybeHelper = this.minutesLeft.keySet().stream().filter(TA::isFree).findFirst();
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if(maybeHelper.isEmpty()) {
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Utils.tryWait(); // nobody is free; wait a short time
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continue;
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}
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TA helper = maybeHelper.orElseThrow();
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// Who to see next?
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Student nextStudent = queue.poll();
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// Help the student
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System.out.println(Utils.timestamp()+" Dispatcher: Hi "+nextStudent+"; you'll be seen by "+helper);
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try {
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helper.seeStudent(nextStudent);
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} catch (TABusyException e) {
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// We hope this won't happen, but if this class had a bug in it, or a different
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// thread were possibly assigning students, or if we had implemented a TA timeout,
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// this would be possible...
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System.out.println("Unexpected behavior: TA became busy while assigning student! Re-adding student to queue.");
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queue.addFirst(nextStudent); // a Deque lets us add at the front or the back
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}
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} else {
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System.out.println(Utils.timestamp()+" Dispatcher ("+studentsHelped+" helped so far): Nobody waiting in queue, will check again shortly.");
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Utils.tryWait();
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}
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}
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}
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public static void helpedAStudent() {
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studentsHelped++;
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}
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}

‎F25/sep16_refinements/exercise/src/main/java/edu/brown/cs32/livecode/dispatcher/Main.java‎

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package edu.brown.cs32.livecode.dispatcher;
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import edu.brown.cs32.livecode.records.Student;
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import edu.brown.cs32.livecode.records.TA;
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import java.util.*;
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/**
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* Show the (incomplete) dispatcher example
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*/
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public class Main {
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public static void main(String[] args) {
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// Not all Lists implement Queue. LinkedList does, ArrayList does not.
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Deque<Student> queue = new LinkedList<>(Arrays.asList(
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new Student("Nim", "project1", 1000),
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new Student("Alice", "project1", 1000),
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new Student("Bob", "project1", 1000),
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new Student("Charli", "project2", 1000),
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new Student("Boatswain", "project2", 1000),
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new Student("Bucky", "project3", 1000)));
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HoursDispatcher dispatcher = new HoursDispatcher(queue);
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// Random Spring '23 TA names, for demo purposes:
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dispatcher.addTA(new TA("Erica", "project1", queue), 110);
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dispatcher.addTA(new TA("Orion", "project2", queue), 50);
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dispatcher.dispatch();
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}
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}

‎F25/sep16_refinements/exercise/src/main/java/edu/brown/cs32/livecode/dispatcher/utils/TABusyException.java‎

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package edu.brown.cs32.livecode.dispatcher.utils;
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public class TABusyException extends Exception {
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public TABusyException() {
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}
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}

‎F25/sep16_refinements/exercise/src/main/java/edu/brown/cs32/livecode/dispatcher/utils/Utils.java‎

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package edu.brown.cs32.livecode.dispatcher.utils;
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import java.time.LocalTime;
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import java.time.format.DateTimeFormatter;
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public class Utils {
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private Utils() {} // no constructor
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final static private DateTimeFormatter fmt = DateTimeFormatter.ofPattern("hh:mm:ss:SSS");
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public static String timestamp() {
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return fmt.format(LocalTime.now());
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}
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/** The number of milliseconds to wait if no progress can be made. */
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static final int SLEEP_DELAY_MS = 3000;
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/** Exit code: the application thread has unexpectedly terminated. */
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static final int ERR_THREAD_TERMINATED = 1;
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/** The application waits before trying again. */
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public static void tryWait() {
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try {
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Thread.sleep(SLEEP_DELAY_MS);
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} catch(InterruptedException e) {
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// The application thread has been interrupted. Stop the app.
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System.out.println("Dispatcher terminated. Stopping.");
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System.exit(ERR_THREAD_TERMINATED); // Exit the application with error status
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}
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}
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}

‎F25/sep16_refinements/exercise/src/main/java/edu/brown/cs32/livecode/records/Student.java‎

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package edu.brown.cs32.livecode.records;
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/** A student-at-hours record. Notice that we can customize the functionality
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* that the record invisibly generates for us: we're replacing toString(). */
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public record Student(String name, String projectID, Integer problem_needs_ms) {
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@Override
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public String toString() {
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return this.name;
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}
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}

‎F25/sep16_refinements/exercise/src/main/java/edu/brown/cs32/livecode/records/TA.java‎

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package edu.brown.cs32.livecode.records;
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import edu.brown.cs32.livecode.dispatcher.HoursDispatcher;
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import edu.brown.cs32.livecode.dispatcher.utils.TABusyException;
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import edu.brown.cs32.livecode.dispatcher.utils.Utils;
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import java.util.Deque;
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/** A TA record, with some functionality. Because we need to have internal
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* state (at least, designed like this) we have to use a class, not a record.
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*/
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public class TA {
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final private String name;
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final private String specialty;
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final private Deque<Student> replaceIn;
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public TA(String name, String specialty, Deque<Student> replaceIn) {
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this.name = name;
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this.specialty = specialty;
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this.replaceIn = replaceIn;
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}
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public String getName() {
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return name;
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}
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private Student helping = null;
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public void seeStudent(Student student) throws TABusyException {
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if(this.helping != null)
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throw new TABusyException();
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this.helping = student;
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System.out.println(Utils.timestamp()+" "+name+ " says: Hello "+helping+"!");
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try {
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// Help the student, however long they need
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Thread.sleep(helping.problem_needs_ms());
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} catch (InterruptedException e) {
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// Shouldn't happen, but in case it does due to OS issues etc.:
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System.out.println(this.name+" was interrupted; had to stop helping.");
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this.replaceIn.addFirst(helping);
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}
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System.out.println(name+ " says: Goodbye "+helping+", I hope that helped!!");
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HoursDispatcher.helpedAStudent();
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helping = null;
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}
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@Override
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public String toString() {
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return name;
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}
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public boolean isFree() {
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return helping == null;
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}
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}

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