Create database for school system

Here's a basic example of a database for a school system in Java using MySQL as the database management system. This example includes classes for `Student`, `Teacher`, `Course`, `Grade`, and `School`.

**Database Schema:**

```sql
CREATE TABLE School (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL,
  address VARCHAR(255) NOT NULL
);

CREATE TABLE Teacher (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL,
  email VARCHAR(255) NOT NULL,
  school_id INT,
  FOREIGN KEY (school_id) REFERENCES School(id)
);

CREATE TABLE Course (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL,
  description VARCHAR(255) NOT NULL,
  teacher_id INT,
  FOREIGN KEY (teacher_id) REFERENCES Teacher(id)
);

CREATE TABLE Student (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL,
  email VARCHAR(255) NOT NULL,
  school_id INT,
  FOREIGN KEY (school_id) REFERENCES School(id)
);

CREATE TABLE Grade (
  id INT PRIMARY KEY AUTO_INCREMENT,
  student_id INT,
  course_id INT,
  grade DECIMAL(3, 2) NOT NULL,
  FOREIGN KEY (student_id) REFERENCES Student(id),
  FOREIGN KEY (course_id) REFERENCES Course(id)
);
```

**Java Classes:**

```java
// School.java
public class School {
    private int id;
    private String name;
    private String address;

    public School(int id, String name, String address) {
        this.id = id;
        this.name = name;
        this.address = address;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getAddress() {
        return address;
    }
}

// Teacher.java
public class Teacher {
    private int id;
    private String name;
    private String email;
    private School school;

    public Teacher(int id, String name, String email, School school) {
        this.id = id;
        this.name = name;
        this.email = email;
        this.school = school;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getEmail() {
        return email;
    }

    public School getSchool() {
        return school;
    }
}

// Course.java
public class Course {
    private int id;
    private String name;
    private String description;
    private Teacher teacher;

    public Course(int id, String name, String description, Teacher teacher) {
        this.id = id;
        this.name = name;
        this.description = description;
        this.teacher = teacher;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getDescription() {
        return description;
    }

    public Teacher getTeacher() {
        return teacher;
    }
}

// Student.java
public class Student {
    private int id;
    private String name;
    private String email;
    private School school;

    public Student(int id, String name, String email, School school) {
        this.id = id;
        this.name = name;
        this.email = email;
        this.school = school;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getEmail() {
        return email;
    }

    public School getSchool() {
        return school;
    }
}

// Grade.java
public class Grade {
    private int id;
    private Student student;
    private Course course;
    private double grade;

    public Grade(int id, Student student, Course course, double grade) {
        this.id = id;
        this.student = student;
        this.course = course;
        this.grade = grade;
    }

    public int getId() {
        return id;
    }

    public Student getStudent() {
        return student;
    }

    public Course getCourse() {
        return course;
    }

    public double getGrade() {
        return grade;
    }
}
```

**Database Connection and CRUD Operations:**

```java
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class SchoolDatabase {
    private Connection connection;

    public SchoolDatabase(String dbUrl, String dbUser, String dbPassword) {
        try {
            connection = DriverManager.getConnection(dbUrl, dbUser, dbPassword);
        } catch (SQLException e) {
            System.out.println("Error connecting to database: " + e.getMessage());
        }
    }

    public void createSchool(School school) {
        try {
            String query = "INSERT INTO School (name, address) VALUES (?, ?)";
            PreparedStatement statement = connection.prepareStatement(query);
            statement.setString(1, school.getName());
            statement.setString(2, school.getAddress());
            statement.executeUpdate();
        } catch (SQLException e) {
            System.out.println("Error creating school: " + e.getMessage());
        }
    }

    public void createTeacher(Teacher teacher) {
        try {
            String query = "INSERT INTO Teacher (name, email, school_id) VALUES (?, ?, ?)";
            PreparedStatement statement = connection.prepareStatement(query);
            statement.setString(1, teacher.getName());
            statement.setString(2, teacher.getEmail());
            statement.setInt(3, teacher.getSchool().getId());
            statement.executeUpdate();
        } catch (SQLException e) {
            System.out.println("Error creating teacher: " + e.getMessage());
        }
    }

    public void createCourse(Course course) {
        try {
            String query = "INSERT INTO Course (name, description, teacher_id) VALUES (?, ?, ?)";
            PreparedStatement statement = connection.prepareStatement(query);
            statement.setString(1, course.getName());
            statement.setString(2, course.getDescription());
            statement.setInt(3, course.getTeacher().getId());
            statement.executeUpdate();
        } catch (SQLException e) {
            System.out.println("Error creating course: " + e.getMessage());
        }
    }

    public void createStudent(Student student) {
        try {
            String query = "INSERT INTO Student (name, email, school_id) VALUES (?, ?, ?)";
            PreparedStatement statement = connection.prepareStatement(query);
            statement.setString(1, student.getName());
            statement.setString(2, student.getEmail());
            statement.setInt(3, student.getSchool().getId());
            statement.executeUpdate();
        } catch (SQLException e) {
            System.out.println("Error creating student: " + e.getMessage());
        }
    }

    public void createGrade(Grade grade) {
        try {
            String query = "INSERT INTO Grade (student_id, course_id, grade) VALUES (?, ?, ?)";
            PreparedStatement statement = connection.prepareStatement(query);
            statement.setInt(1, grade.getStudent().getId());
            statement.setInt(2, grade.getCourse().getId());
            statement.setDouble(3, grade.getGrade());
            statement.executeUpdate();
        } catch (SQLException e) {
            System.out.println("Error creating grade: " + e.getMessage());
        }
    }

    public void closeConnection() {
        try {
            connection.close();
        } catch (SQLException e) {
            System.out.println("Error closing connection: " + e.getMessage());
        }
    }
}
```

**Example Usage:**

```java
public class Main {
    public static void main(String[] args) {
        SchoolDatabase database = new SchoolDatabase("jdbc:mysql://localhost:3306/school", "username", "password");

        School school = new School(1, "Example School", "123 Main St");
        database.createSchool(school);

        Teacher teacher = new Teacher(1, "John Doe", "john.doe@example.com", school);
        database.createTeacher(teacher);

        Course course = new Course(1, "Math", "Math course", teacher);
        database.createCourse(course);

        Student student = new Student(1, "Jane Doe", "jane.doe@example.com", school);
        database.createStudent(student);

        Grade grade = new Grade(1, student, course, 85.0);
        database.createGrade(grade);

        database.closeConnection();
    }
}
```

This is a basic example of a school database system in Java. It includes classes for `School`, `Teacher`, `Course`, `Student`, and `Grade`, as well as a `SchoolDatabase` class for interacting with the database. The example usage demonstrates how to create a school, teacher, course, student, and grade, and then close the database connection.