将第3题修改为4层架构，写出对应代码

要将第3题中的功能修改为4层架构（表示层、业务逻辑层、数据访问层和实体层），可以按照以下步骤进行设计和实现：

### 1. 实体层 (Entity Layer)
定义出版社的实体类 `Publisher`。

public class Publisher {
    private int id;
    private String name;
    private String postalCode;
    private String address;
    private String phoneNumber;

    // 构造函数
    public Publisher() {}

    public Publisher(int id, String name, String postalCode, String address, String phoneNumber) {
        this.id = id;
        this.name = name;
        this.postalCode = postalCode;
        this.address = address;
        this.phoneNumber = phoneNumber;
    }

    // Getter 和 Setter 方法
    public int getId() { return id; }
    public void setId(int id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public String getPostalCode() { return postalCode; }
    public void setPostalCode(String postalCode) { this.postalCode = postalCode; }
    public String getAddress() { return address; }
    public void setAddress(String address) { this.address = address; }
    public String getPhoneNumber() { return phoneNumber; }
    public void setPhoneNumber(String phoneNumber) { this.phoneNumber = phoneNumber; }
}

### 2. 数据访问层 (Data Access Layer)
定义数据访问接口 `PublisherDAO` 和其实现类 `PublisherDAOImpl`。

import java.util.List;

public interface PublisherDAO {
    boolean deletePublisher(int id);
    List<Publisher> getAllPublishers();
}

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class PublisherDAOImpl implements PublisherDAO {
    private Connection getConnection() throws SQLException {
        // 假设使用 JDBC 连接数据库
        String url = "jdbc:mysql://localhost:3306/publisher_management";
        String user = "root";
        String password = "password";
        return DriverManager.getConnection(url, user, password);
    }

    @Override
    public boolean deletePublisher(int id) {
        try (Connection conn = getConnection()) {
            String sql = "DELETE FROM publisher WHERE id = ?";
            PreparedStatement stmt = conn.prepareStatement(sql);
            stmt.setInt(1, id);
            int rowsAffected = stmt.executeUpdate();
            return rowsAffected > 0;
        } catch (SQLException e) {
            e.printStackTrace();
            return false;
        }
    }

    @Override
    public List<Publisher> getAllPublishers() {
        List<Publisher> publishers = new ArrayList<>();
        try (Connection conn = getConnection()) {
            String sql = "SELECT * FROM publisher";
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery(sql);
            while (rs.next()) {
                Publisher publisher = new Publisher(
                        rs.getInt("id"),
                        rs.getString("name"),
                        rs.getString("postal_code"),
                        rs.getString("address"),
                        rs.getString("phone_number")
                );
                publishers.add(publisher);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return publishers;
    }
}

### 3. 业务逻辑层 (Business Logic Layer)
定义业务逻辑类 `PublisherService`。

public class PublisherService {
    private PublisherDAO publisherDAO;

    public PublisherService(PublisherDAO publisherDAO) {
        this.publisherDAO = publisherDAO;
    }

    public boolean deletePublisher(int id) {
        return publisherDAO.deletePublisher(id);
    }

    public List<Publisher> getAllPublishers() {
        return publisherDAO.getAllPublishers();
    }
}

### 4. 表示层 (Presentation Layer)
定义图形界面类 `DeletePublisherUI`。

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class DeletePublisherUI extends JFrame {
    private JTextField idField;
    private JButton deleteButton;
    private JLabel resultLabel;
    private PublisherService publisherService;

    public DeletePublisherUI(PublisherService publisherService) {
        this.publisherService = publisherService;
        setTitle("删除出版社");
        setSize(400, 200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel = new JPanel();
        panel.setLayout(new GridLayout(3, 2));

        panel.add(new JLabel("出版社编号:"));
        idField = new JTextField();
        panel.add(idField);

        deleteButton = new JButton("删除");
        deleteButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                int id = Integer.parseInt(idField.getText());
                if (publisherService.deletePublisher(id)) {
                    resultLabel.setText("删除成功！");
                } else {
                    resultLabel.setText("删除失败！");
                }
            }
        });
        panel.add(deleteButton);

        resultLabel = new JLabel("");
        panel.add(resultLabel);

        add(panel);
        setVisible(true);
    }

    public static void main(String[] args) {
        PublisherDAO publisherDAO = new PublisherDAOImpl();
        PublisherService publisherService = new PublisherService(publisherDAO);
        new DeletePublisherUI(publisherService);
    }
}

以上代码实现了将第3题的功能修改为4层架构的设计。每一层都有明确的责任分工，使得代码更加模块化和易于维护。