根据以下要求：Instead of using a binary file to save the arraylist of points, change the savaData method and the constructor of the Model class to use a database to write / read the coordinates of all the points. Use XAMPP and phpMyAdmin to create a database called "java" with a table called "points" that has two integer columns x and y (in addition to the ID primary key). Hint: make sure you delete all the old point coordinates from the database before inserting new ones. Hint: use phpMyAdmin to check what is stored in the database. Use the Test class to run all the tests for the software and check that all the tests still work. Use the Start class to run the software and check that closing the software correctly saves the point coordinates in the database (use phpMyAdmin to check the content of the database). Run the software again and check that all the points from the previous run are correctly displayed，修改下述代码：public class Model implements Serializable { private ArrayList<Point> points; private ArrayList<ModelListener> listeners; private static final String FILE_NAME = "points.bin"; public Model() { points = new ArrayList<Point>(); listeners = new ArrayList<ModelListener>(); // Read points from file if it exists File file = new File(FILE_NAME); if (file.exists()) { try { ObjectInputStream in = new ObjectInputStream(new FileInputStream(file)); points = (ArrayList<Point>) in.readObject(); in.close(); } catch (IOException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } } public void addListener(ModelListener l) { listeners.add(l); } public ArrayList<Point> getPoints() { return points; } public void addPoint(Point p) { points.add(p); notifyListeners(); // points changed so notify the listeners. saveData(); // save point to file } public void clearAllPoints() { points.clear(); notifyListeners(); // points changed so notify the listeners. saveData(); // save empty list to file } public void deleteLastPoint() { if (points.size() > 0) { points.remove(points.size() - 1); notifyListeners(); // points changed so notify the listeners. saveData(); // save updated list to file } } private void notifyListeners() { for (ModelListener l : listeners) { l.update(); // Tell the listener that something changed. } } public int numberOfPoints() { return points.size(); } public void saveData() { try { ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(FILE_NAME)); out.writeObject(points); out.close(); } catch (IOException e) { e.printStackTrace(); } }

public class Model {
private ArrayList<Point> points;
private ArrayList<ModelListener> listeners;
private static final String DB_URL = "jdbc:mysql://localhost/java";
private static final String DB_USER = "root";
private static final String DB_PASSWORD = "";

public Model() {
points = new ArrayList<Point>();
listeners = new ArrayList<ModelListener>();
// Read points from database
try {
Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
Statement stmt = conn.createStatement();
String sql = "SELECT * FROM points";
ResultSet rs = stmt.executeQuery(sql);
while (rs.next()) {
int x = rs.getInt("x");
int y = rs.getInt("y");
Point p = new Point(x, y);
points.add(p);
}
rs.close();
stmt.close();
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}

public void addListener(ModelListener l) {
listeners.add(l);
}

public ArrayList<Point> getPoints() {
return points;
}

public void addPoint(Point p) {
points.add(p);
notifyListeners(); // points changed so notify the listeners.
saveData(); // save point to database
}

public void clearAllPoints() {
points.clear();
notifyListeners(); // points changed so notify the listeners.
saveData(); // save empty list to database
}

public void deleteLastPoint() {
if (points.size() > 0) {
points.remove(points.size() - 1);
notifyListeners(); // points changed so notify the listeners.
saveData(); // save updated list to database
}
}

private void notifyListeners() {
for (ModelListener l : listeners) {
l.update(); // Tell the listener that something changed.
}
}

public int numberOfPoints() {
return points.size();
}

public void saveData() {
try {
Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
Statement stmt = conn.createStatement();
String sql = "DELETE FROM points";
stmt.executeUpdate(sql);
for (Point p : points) {
sql = "INSERT INTO points (x, y) VALUES (" + p.x + ", " + p.y + ")";
stmt.executeUpdate(sql);
}
stmt.close();
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}