根据以下要求：Instead of using a text file to save all the point coordinates one by one, change the savaData method and the constructor of the Model class to use object serialization and a binary file called "points.bin" to write / read the whole arraylist of points to / from the file in one operation.修改下述代码：import java.awt.Point; import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.File; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.io.PrintWriter; import java.util.ArrayList; import java.util.Scanner; public class Model { private ArrayList<Point> points; private ArrayList<ModelListener> listeners; public Model() { points = new ArrayList<Point>(); listeners = new ArrayList<ModelListener>(); // Read points from file if it exists File file = new File("points.txt"); if (file.exists()) { try { Scanner scanner = new Scanner(file); while (scanner.hasNextLine()) { String[] coordinates = scanner.nextLine().split(" "); int x = (int) Double.parseDouble(coordinates[0]); int y = (int) Double.parseDouble(coordinates[1]); points.add(new Point(x, y)); } scanner.close(); } catch (FileNotFoundException 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 { FileWriter writer = new FileWriter("points.txt"); for (Point p : points) { writer.write(p.x + " " + p.y + "\n"); } writer.close(); } catch (IOException e) { e.printStackTrace(); } }

以下是修改后的代码：

import java.awt.Point;
import java.io.*;

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();
}
}
}

这里我们使用了Java的序列化机制来保存整个ArrayList对象，同时将数据保存到了一个二进制文件中（名为"points.bin"）。在构造函数中，我们首先检查是否存在该文件，如果存在，则通过ObjectInputStream读取该文件并将ArrayList对象恢复到程序中。在saveData()方法中，我们使用ObjectOutputStream将整个ArrayList对象写入文件。注意：我们还必须将Model类实现Serializable接口来支持序列化。