Credit for work:

This is what I have, but I keep getting errors:

Exception in thread "main" java.util.ConcurrentModificationException

at java.util.HashMap$HashIterator.nextNode(Unknown Source)

at java.util.HashMap$KeyIterator.next(Unknown Source)

at airlines.FlightNet.removeAndDisconnect(FlightNet.java:42)

at airlines.AirGrader.checkFlightNet(AirGrader.java:258)

at airlines.AirGrader.main(AirGrader.java:301)

Airport.java

package airlines;

import java.util.*;

public class Airport implements Comparable {

private String name;

private int x;

private int y;

private Set connections; // all airports with a direct route to/from this airport

public Airport(String name, int x, int y) {

this.name = name;

this.x = x;

this.y = y;

connections = new TreeSet<>();

}

public String getName() {

return name;

}

public int getX() {

return x;

}

public int getY() {

return y;

}

public List getConnections() {

return new ArrayList<>(connections);

}

// Adds that airport to the list of connections.

public void connectTo(Airport that) {

connections.add(that);

}

//

// Does nothing if this airport is not connected to that.

//

public void disconnectFrom(Airport that) {

if (!connections.contains(that))

return;

connections.remove(that);

}

// Use best practice.

public boolean equals(Object x) {

Airport that = (Airport) x;

return this.compareTo(that) == 0;

}

// Just compare by airport name.

public int compareTo(Airport that) {

int getCmp = this.getName().compareTo(that.getName());

return getCmp;

}

public boolean isConnectedTo(Airport that) {

if (connections.contains(that))

return true;

return false;

}

public String toString() {

return "Airport " + name + " @(" + x + "," + y + ")";

}

}

FlightNet.java

package airlines;

import java.util.HashSet;

import java.util.Iterator;

import java.util.List;

import java.util.concurrent.CopyOnWriteArrayList;

public class FlightNet extends HashSet {

public boolean nameIsAvailable(String name) {

for (Airport b : this) {

if (b.getName().equals(name)) {

return false;

}

}

return true;

}

public void connect(Airport a1, Airport a2) {

a1.connectTo(a2);

a2.connectTo(a1);

}

public void disconnect(Airport a1, Airport a2) {

a1.disconnectFrom(a2);

a2.disconnectFrom(a1);

}

public void removeAndDisconnect(Airport removeMe) {

for (Airport b : this) {

if (b.isConnectedTo(removeMe)) {

b.disconnectFrom(removeMe);

this.remove(removeMe);

}

}

}

public Airport getAirportNearXY(int x, int y, int maximumDistance) {

for (Airport b : this) {

double travelDistance = Math.hypot(x - b.getX(), y - b.getY());

if (travelDistance <= maximumDistance) {

return b;

}

}

return null;

}

}

RoutesPanel.java (dont need to edit)

package airlines;

import java.io.*;

import java.util.*;

import java.awt.*;

import java.awt.event.*;

import java.awt.geom.*;

import java.awt.image.BufferedImage;

import javax.imageio.ImageIO;

import javax.swing.*;

public class RoutesPanel extends JPanel

{

private final static Font FONT = new Font("SansSerif", Font.PLAIN, 12);

private final static int CLICK_RADIUS = 11;

private final static Color UNARMED_COLOR = Color.BLACK;

private final static Color ARMED_FOR_CONNECTION_COLOR = new Color(0, 200, 0);

private final static Color ARMED_FOR_DELETION_COLOR = Color.RED;

private final static File MAP_FILE = new File("pix/usmap.jpg");

private final static Color WHITEWASH_COLOR = new Color(255, 255, 255, 200);

private final static Stroke ROUTE_STROKE = new BasicStroke(2);

private FlightNet net;

private Airport armedAirport;

private BufferedImage usMapImage;

RoutesPanel()

{

try

{

usMapImage = ImageIO.read(MAP_FILE);

}

catch (IOException x)

{

sop("Can't read map image file " + MAP_FILE.getAbsolutePath());

System.exit(1);

}

net = new FlightNet();

setPreferredSize(new Dimension(usMapImage.getWidth()/2, usMapImage.getHeight()/2));

MLis lis = new MLis();

addMouseListener(lis);

addMouseMotionListener(lis);

}

private class MLis extends MouseAdapter

{

@Override

public void mouseClicked(MouseEvent e)

{

Airport clickedAirport = net.getAirportNearXY(e.getX(), e.getY(), CLICK_RADIUS);

// First of 1 or 2 clicks.

if (armedAirport == null)

{

if (clickedAirport == null)

{

// Click in empty space to create new airport.

armedAirport = null;

NameDia dia = new NameDia(e.getX(), e.getY());

dia.setVisible(true);

}

else

{

// Click on existing airport to arm it.

armedAirport = clickedAirport;

}

}

// Second of 2 clicks

else

{

if (clickedAirport == null)

{

// 2nd click in empty space to cancel operation.

armedAirport = null;

}

else if (clickedAirport == armedAirport)

{

// 2nd click on armed airport to delete it.

net.removeAndDisconnect(armedAirport);

armedAirport = null;

}

else if (clickedAirport.isConnectedTo(armedAirport))

{

// 2nd click on connected airport to delete the connection.

net.disconnect(armedAirport, clickedAirport);

armedAirport = null;

}

else

{

// 2nd click on unconnected airport to connect it.

net.connect(armedAirport, clickedAirport);

armedAirport = null;

}

}

repaint();

}

} // MLis

private class NameDia extends JDialog implements ActionListener

{

private int x;

private int y;

private JTextField tf;

private JButton okBtn;

private JButton cancelBtn;

NameDia(int x, int y)

{

this.x = x;

this.y = y;

JPanel pan = new JPanel();

pan.add(new JLabel("3-letter name: "));

tf = new JTextField(4);

tf.addActionListener(this);

pan.add(tf);

add(pan, BorderLayout.NORTH);

pan = new JPanel();

okBtn = new JButton("Ok");

okBtn.addActionListener(this);

pan.add(okBtn);

cancelBtn = new JButton("Cancel");

cancelBtn.addActionListener(this);

pan.add(cancelBtn);

add(pan, BorderLayout.SOUTH);

pack();

setModal(true);

}

@Override

public void actionPerformed(ActionEvent e)

{

if (e.getSource() == cancelBtn)

{

setVisible(false);

}

else

{

String name = tf.getText().trim();

if (name.length() != 3)

{

JOptionPane.showMessageDialog(this, "Name must be 3 letters");

return;

}

if (!net.nameIsAvailable(name))

{

JOptionPane.showMessageDialog(this, "Name is in use");

return;

}

setVisible(false);

net.add(new Airport(name, x, y));

repaint();

}

}

} // NameDia

public void paintComponent(Graphics g)

{

// Background.

g.drawImage(usMapImage, 0, 0, getWidth(), getHeight(), this);

// Whitewash.

g.setColor(WHITEWASH_COLOR);

g.fillRect(0, 0, getWidth(), getHeight());

// Existing routes in black. If an airport is armed, some will get overdrawn.

g.setColor(UNARMED_COLOR);

Graphics2D g2 = (Graphics2D)g;

g2.setStroke(ROUTE_STROKE);

for (Airport a: net)

for (Airport dest: a.getConnections())

g.drawLine(a.getX(), a.getY(), dest.getX(), dest.getY());

// Routes that are armed for deletion.

if (armedAirport != null)

{

g.setColor(ARMED_FOR_DELETION_COLOR);

for (Airport dest: armedAirport.getConnections())

g.drawLine(armedAirport.getX(), armedAirport.getY(), dest.getX(), dest.getY());

}

// Routes that are armed for connection.

if (armedAirport != null)

{

g.setColor(ARMED_FOR_CONNECTION_COLOR);

for (Airport dest: net)

{

if (dest == armedAirport)

continue;

if (armedAirport.getConnections().contains(dest))

continue;

g.drawLine(armedAirport.getX(), armedAirport.getY(), dest.getX(), dest.getY());

}

}

// Airports

g.setFont(FONT);

for (Airport a: net)

if (a != armedAirport)

paintAirport(g, a);

if (armedAirport != null)

paintAirport(g, armedAirport);

}

private void paintAirport(Graphics g, Airport a)

{

int x = a.getX();

int y = a.getY();

boolean armed = a == armedAirport;

g.setColor(armed ? ARMED_FOR_DELETION_COLOR : UNARMED_COLOR);

g.fillOval(x-2, y-2, 5, 5);

g.drawOval(x-5, y-5, 11, 11);

int sw = g.getFontMetrics().stringWidth(a.getName());

g.drawString(a.getName(), x-sw/2, y+18);

}

static void sop(Object x) { System.out.println(x); }

public static void main(String[] args)

{

JFrame frame = new JFrame();

frame.add(new RoutesPanel());

frame.pack();

frame.setLocation(100, 100);

frame.setVisible(true);

}

}

AirGrader.java (dont need to edit)

package airlines;

import java.lang.reflect.*;

import java.util.*;

public class AirGrader

{

private final static Airport AAA = new Airport("AAA", 10, 20);

private final static Airport BBB1 = new Airport("BBB", 10, 20);

private final static Airport BBB2 = new Airport("BBB", 10, 20);

private final static Airport BBB3 = new Airport("BBB", 99, 88);

private final static Airport CCC = new Airport("CCC", 10, 20);

private final static Airport DDD = new Airport("DDD", 10, 20);

private final static Airport MMM = new Airport("MMM", 10, 20);

private final static Airport NNN = new Airport("NNN", 10, 20);

private static void checkAirport()

{

// Class.

Class airportClass = null;

try

{

airportClass = Class.forName("airlines.Airport");

}

catch (ClassNotFoundException x)

{

abortZeroPoints("No airlines.Airport class");

}

// Implements Comparable

Class[] interfaces = airportClass.getInterfaces();

boolean hasComparable = false;

for (Class c: interfaces)

{

if (c.getName().equals("java.lang.Comparable"))

{

hasComparable = true;

break;

}

}

if (!hasComparable)

abortZeroPoints("Airport doesn't implement Comparable");

// equals() calls compareTo()

SubAirport sub1 = new SubAirport("XXX", 0, 0);

SubAirport sub2 = new SubAirport("ZZZ", 0, 0);

sub1.equals(sub2);

if (!sub1.compareToWasCalled)

abortZeroPoints("In Airport, equals() doesn't call compareTo => Not best practice");

// equals()

checkEquals(AAA, BBB1, false);

checkEquals(BBB1, BBB2, true);

checkEquals(BBB1, BBB3, true);

// compareTo()

checkCompareTo(AAA, BBB1, -1);

checkCompareTo(BBB1, BBB2, 0);

checkCompareTo(BBB1, BBB3, 0);

// getConnections() should return sorted airports.

Airport that = new Airport("ZZZ", 1, 0);

Airport[] addOrder = { CCC, DDD, BBB1, AAA };

Airport[] expectOrder = { AAA, BBB1, CCC, DDD };

for (Airport a: addOrder)

that.connectTo(a);

List conns = that.getConnections();

String errPiece = "Added in this order:";

for (Airport a: addOrder)

errPiece += " " + a;

errPiece += " getConnections() returned:";

for (Airport a: conns)

errPiece += " " + a;

errPiece += " expected:";

for (Airport a: expectOrder)

errPiece += " " + a;

if (conns.size() != 4)

abortZeroPoints("Wrong number of airports: " + errPiece);

for (int i=0; i<4; i++)

if (!conns.get(i).equals(expectOrder[i]))

abortZeroPoints("getConnections returned airports in wrong order " + errPiece);

// isConnectedTo.

that = new Airport("XYZ", 0, 0);

that.connectTo(CCC);

that.connectTo(DDD);

Airport[] connOrder = { CCC, DDD };

Airport[] checks = { CCC, DDD, MMM, NNN };

boolean[] bExpect = { true, true, false, false };

for (Airport a: connOrder)

that.connectTo(a);

boolean trouble = false;

for (int i=0; i<4; i++)

if (that.isConnectedTo(checks[i]) != bExpect[i])

trouble = true;

if (trouble)

{

String err = "Connected an airport to " + CCC + " and " + DDD;

for (int i=0; i<4; i++)

err += " isConnectedTo(" + checks[i] + ") returned " + that.isConnectedTo(checks[i]) + ", expected " + bExpect[i];

abortZeroPoints(err);

}

}

private static void checkEquals(Airport a1, Airport a2, boolean expect)

{

boolean result = a1.equals(a2);

if (result != expect)

abortZeroPoints("equals() on " + a1 + " and " + a2 + " returned " + result + ", should be " + expect);

result = a2.equals(a1);

if (result != expect)

abortZeroPoints("equals() on " + a2 + " and " + a1 + " returned " + result + ", should be " + expect);

}

private static void checkCompareTo(Airport a1, Airport a2, int expectSignum)

{

int result = a1.compareTo(a2);

if (Math.signum(result) != expectSignum)

abortZeroPoints("compareTo() on " + a1 + " and " + a2 + " returned " + result + ", should be " + signumToString(expectSignum));

result = a2.compareTo(a1);

expectSignum *= -1;

if (Math.signum(result) != expectSignum)

abortZeroPoints("compareTo() on " + a2 + " and " + a1 + " returned " + result + ", should be " + signumToString(expectSignum));

}

private static String signumToString(int n)

{

if (n == 0)

return "0";

else if (n < 0)

return "<0";

else

return ">0";

}

private static class SubAirport extends Airport

{

boolean compareToWasCalled;

SubAirport(String name, int x, int y)

{

super(name, x, y);

}

public int compareTo(Airport that)

{

compareToWasCalled = true;

return 0;

}

}

private static void checkFlightNet()

{

// Extends HashSet?

Class fnClass = null;

try

{

fnClass = Class.forName("airlines.FlightNet");

}

catch (ClassNotFoundException x)

{

abortZeroPoints("No airlines.FlightNet class");

}

Class supeClass = fnClass.getSuperclass();

try

{

Class hsClass = Class.forName("java.util.HashSet");

if (hsClass != supeClass)

abortZeroPoints("FlightNet doesn't extend HashSet");

}

catch (ClassNotFoundException x) { } // Shouldn't happen, ignore if it does

// Add

FlightNet that = new FlightNet();

Airport[] adds = { AAA, BBB1, CCC, DDD };

String addsErr = "Added to a FlightNet:";

for (Airport a: adds)

{

that.add(a);

addsErr += " " + a;

}

// Name availability

for (Airport a: adds)

{

if (that.nameIsAvailable(a.getName()))

{

String err = addsErr + " Then nameIsAvailable(" + a.getName() + ") returned true";

abortZeroPoints(err);

}

}

if (!that.nameIsAvailable("SFO"))

{

String err = addsErr + " Then nameIsAvailable(\"SFO\") returned false";

abortZeroPoints(err);

}

// Connection

that = new FlightNet();

Airport sfo = new Airport("SFO", 0, 0);

Airport jfk = new Airport("JFK", 100, 100);

that.add(sfo);

that.add(jfk);

that.connect(sfo, jfk);

if (sfo.isConnectedTo(jfk) == false || jfk.isConnectedTo(sfo) == false)

{

String err = "Created a FlightNet fn, then fn.connect(sfo, jfk); ";

err += "Then sfo.isConnectedTo(jfk) returned " + sfo.isConnectedTo(jfk) + " and ";

err += "jfk.isConnectedTo(sfo) returned " + jfk.isConnectedTo(sfo) + " Both should return true";

abortZeroPoints(err);

}

Airport sea = new Airport("SEA", 200, 200);

that.add(sea);

that.connect(sfo, sea);

if (sea.isConnectedTo(jfk))

{

String err = "Created a FlightNet fn, then fn.connect(sfo, jfk); fn.connect(sfo, sea); ";

err += "Then sea.isConnectedTo(jfk) returned true";

abortZeroPoints(err);

}

if (jfk.isConnectedTo(sea))

{

String err = "Created a FlightNet fn, then fn.connect(sfo, jfk); fn.connect(sfo, sea); ";

err += "Then jfk.isConnectedTo(sea) returned true";

abortZeroPoints(err);

}

// getAirportNearXY

Airport nearest = that.getAirportNearXY(110, 100, 12);

if (nearest != jfk)

{

String err = "FlightNet fn contains SFO at (0, 0), JFK at (100, 100), and SEA at (200, 200) ";

err += "Then that.getAirportNearXY(110, 100, 12) returned " + nearest + ", expected jfk";

abortZeroPoints(err);

}

nearest = that.getAirportNearXY(123456, 123456, 100);

if (nearest != null)

{

String err = "FlightNet fn contains SFO at (0, 0) and JFK at (100, 100) ";

err += "Then that.getAirportNearXY(123456, 123456, 100) returned " + nearest + ", expected null";

abortZeroPoints(err);

}

// removeAndDisconnect.

that.removeAndDisconnect(jfk);

String err = "Created a FlightNet fn, then fn.connect(sfo, jfk); fn.connect(sfo, sea); fn.removeAndDisconnect(jfk); ";

if (that.contains(jfk))

{

err += "Then fn still contains jfk";

abortZeroPoints(err);

}

if (!that.contains(sfo))

{

err += "Then fn no longer contains sfo";

abortZeroPoints(err);

}

if (!that.contains(sea))

{

err += "Then fn no longer contains sea";

abortZeroPoints(err);

}

// Has instance vars?

Field[] fields = fnClass.getDeclaredFields();

if (fields.length > 0)

abortZeroPoints("FlightNet class has " + fields.length + " instance variable(s)");

}

private static void abortZeroPoints(String msg)

{

sop("Zero points: " + msg);

System.exit(1);

}

static void sop(Object x)

{

System.out.println(x);

}

public static void main(String[] args)

{

sop("START");

checkAirport();

checkFlightNet();

sop("DONE");

}

}

Please run the AirGrader to check the grade.

Thank you