1. 自选数据库管理系统创建数据库stu，按照下表的结构创建"student"表： 字段名 Java 数据类型 宽度 SQL 数据类型 id int 10 int Name String 20 Char(20) Sex String 2 Char(2) Age Int 3 Integer id Name Sex Age 1 张小明 男 18 2 李雷 男 19 3 韩梅梅 女 18 4. 将数据表 stu 及其数据操作封装成类， 将数据操作功能封装成类的方法， 通过该类， 借助图形用户界面实现下面功能： (1) 向表中增加记录并显示增加后的所有记录(新增记录的具体数据自定)； (2) 从表中删除 id=1 的记录， 并显示删除后的所有记录； (3) 修改表中记录： 查询条件 id=2，将 name 修改为： 王杰，修改完毕显示所有记录； (4) 查询表中 id=3 的记录并显示。编写该代码

下面是一个示例代码，实现了上述要求：

Student.java：

public class Student {
    private int id;
    private String name;
    private String sex;
    private int age;
    
    public Student(int id, String name, String sex, int age) {
        this.id = id;
        this.name = name;
        this.sex = sex;
        this.age = age;
    }

    // getter and setter methods
    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 getSex() { return sex; }
    public void setSex(String sex) { this.sex = sex; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
    
    public String toString() {
        return "id: " + id + ", name: " + name + ", sex: " + sex + ", age: " + age;
    }
}

StudentDAO.java：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class StudentDAO {
    private String url;
    private String username;
    private String password;
    
    public StudentDAO(String url, String username, String password) {
        this.url = url;
        this.username = username;
        this.password = password;
    }
    
    public void add(Student student) throws SQLException {
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            conn = DriverManager.getConnection(url, username, password);
            String sql = "INSERT INTO student (id, name, sex, age) VALUES (?, ?, ?, ?)";
            stmt = conn.prepareStatement(sql);
            stmt.setInt(1, student.getId());
            stmt.setString(2, student.getName());
            stmt.setString(3, student.getSex());
            stmt.setInt(4, student.getAge());
            stmt.executeUpdate();
        } finally {
            if (stmt != null) { stmt.close(); }
            if (conn != null) { conn.close(); }
        }
    }
    
    public void delete(int id) throws SQLException {
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            conn = DriverManager.getConnection(url, username, password);
            String sql = "DELETE FROM student WHERE id = ?";
            stmt = conn.prepareStatement(sql);
            stmt.setInt(1, id);
            stmt.executeUpdate();
        } finally {
            if (stmt != null) { stmt.close(); }
            if (conn != null) { conn.close(); }
        }
    }
    
    public void update(int id, String name) throws SQLException {
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            conn = DriverManager.getConnection(url, username, password);
            String sql = "UPDATE student SET name = ? WHERE id = ?";
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, name);
            stmt.setInt(2, id);
            stmt.executeUpdate();
        } finally {
            if (stmt != null) { stmt.close(); }
            if (conn != null) { conn.close(); }
        }
    }
    
    public Student findById(int id) throws SQLException {
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            conn = DriverManager.getConnection(url, username, password);
            String sql = "SELECT * FROM student WHERE id = ?";
            stmt = conn.prepareStatement(sql);
            stmt.setInt(1, id);
            rs = stmt.executeQuery();
            if (rs.next()) {
                return new Student(rs.getInt("id"), rs.getString("name"), rs.getString("sex"), rs.getInt("age"));
            }
            return null;
        } finally {
            if (rs != null) { rs.close(); }
            if (stmt != null) { stmt.close(); }
            if (conn != null) { conn.close(); }
        }
    }
    
    public List<Student> findAll() throws SQLException {
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            conn = DriverManager.getConnection(url, username, password);
            String sql = "SELECT * FROM student";
            stmt = conn.prepareStatement(sql);
            rs = stmt.executeQuery();
            List<Student> students = new ArrayList<>();
            while (rs.next()) {
                students.add(new Student(rs.getInt("id"), rs.getString("name"), rs.getString("sex"), rs.getInt("age")));
            }
            return students;
        } finally {
            if (rs != null) { rs.close(); }
            if (stmt != null) { stmt.close(); }
            if (conn != null) { conn.close(); }
        }
    }
}

Main.java：

import java.sql.SQLException;
import java.util.List;
import javax.swing.JOptionPane;

public class Main {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/stu?useSSL=false&serverTimezone=UTC";
        String username = "root";
        String password = "123456";
        StudentDAO dao = new StudentDAO(url, username, password);
        try {
            // add a new student
            Student newStudent = new Student(5, "刘德华", "男", 21);
            dao.add(newStudent);
            List<Student> students = dao.findAll();
            System.out.println("After adding:");
            for (Student student : students) {
                System.out.println(student);
            }
            
            // delete a student by id
            dao.delete(1);
            students = dao.findAll();
            System.out.println("After deleting:");
            for (Student student : students) {
                System.out.println(student);
            }
            
            // update a student's name by id
            dao.update(2, "王杰");
            students = dao.findAll();
            System.out.println("After updating:");
            for (Student student : students) {
                System.out.println(student);
            }
            
            // find a student by id
            Student student = dao.findById(3);
            System.out.println("Student with id=3: " + student);
            
            // display all students
            students = dao.findAll();
            System.out.println("All students:");
            for (Student s : students) {
                System.out.println(s);
            }
            
            // display students in a dialog
            StringBuilder sb = new StringBuilder();
            for (Student s : students) {
                sb.append(s).append("\n");
            }
            JOptionPane.showMessageDialog(null, sb.toString(), "All students", JOptionPane.INFORMATION_MESSAGE);
        } catch (SQLException ex) {
            ex.printStackTrace();
        }
    }
}

这个示例代码使用MySQL数据库，需要先安装MySQL并创建一个名为"stu"的数据库。在运行Main类之前，需要确保MySQL服务已经启动，并修改url、username和password变量为正确的值。