import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Date;

public class HomeworkDbThread extends Thread {
    private ArrayList<HomeworkClass> dataSet = new ArrayList<>();
    private Statement stmt;
    private ThreadCallback callback;

    public HomeworkDbThread(Statement statement, ThreadCallback callback) {
        this.stmt = statement;
        this.callback = callback;
    }

    @Override
    public void run() {
        try {
            String sql = "SELECT id, name, lesson, grade, time FROM class";
            ResultSet rs = stmt.executeQuery(sql);

            while (rs.next()) {
                //getting values
                int id = rs.getInt("id");
                String name = rs.getString("name");
                String lesson = rs.getString("lesson");
                int grade = rs.getInt("grade");
                Date time = rs.getDate("time");

                dataSet.add(new HomeworkClass(
                        id,
                        name,
                        lesson,
                        grade,
                        time
                ));
            }

            if (callback != null)
                callback.onDataFetched(dataSet);
        } catch (SQLException e) {
            if (callback != null)
                callback.onError(e);
        } finally {
            if (callback != null)
                callback.onEnd();
        }
    }
}


import java.util.Date;

public class HomeworkClass {
    private Integer id;
    private String name;
    private String lesson;
    private Integer grade;
    private Date date;

    public HomeworkClass() {
    }

    public HomeworkClass(Integer id, String name, String lesson, Integer grade, Date date) {
        this.id = id;
        this.name = name;
        this.lesson = lesson;
        this.grade = grade;
        this.date = date;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getLesson() {
        return lesson;
    }

    public void setLesson(String lesson) {
        this.lesson = lesson;
    }

    public Integer getGrade() {
        return grade;
    }

    public void setGrade(Integer grade) {
        this.grade = grade;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    @Override
    public String toString() {
        return "HomeworkClass{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", lesson='" + lesson + '\'' +
                ", grade=" + grade +
                ", date=" + date +
                '}';
    }
}


import java.lang.Class;
import java.sql.*;
import java.util.ArrayList;
import java.util.Date;
import java.util.Scanner;

public class Homework {
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    static final String DB_URL = "jdbc:mysql://localhost:3306/students";
    static final String USER = "root";
    static final String PASS = "";

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        Connection conn = null;
        Statement stmt = null;
        String sql;

        //showing information for input
        info();
        int response = in.nextInt();

        try {

            Class.forName(JDBC_DRIVER);
            System.out.println("Connecting to database...");

            conn = DriverManager.getConnection(DB_URL, USER, PASS);
            stmt = conn.createStatement();

            switch (response) {
                case 1: // list all students info
                    Connection finalConn = conn;
                    Statement finalStmt = stmt;

                    ThreadCallback callback = new ThreadCallback() {
                        @Override
                        public void onDataFetched(ArrayList<HomeworkClass> dataSet) {
                            for (HomeworkClass homeworkClass : dataSet) {
                                System.out.println(homeworkClass.toString());
                            }
                        }

                        @Override
                        public void onError(SQLException ex) {
                            ex.printStackTrace();
                        }

                        @Override
                        public void onEnd() {
                            //disconnect from database
                            disconncetDb(finalConn, finalStmt);
                        }
                    };

                    HomeworkDbThread dbThread = new HomeworkDbThread(stmt, callback);
                    dbThread.start();
                    break;

                case 2: // Insert new info
                    ArrayList<HomeworkClass> dataSetForInsert = new ArrayList<>();

                    HomeworkClass homeworkClass = new HomeworkClass();
                    homeworkClass.setName("");

                    System.out.println("Please Enter student's name: ");
                    String newName = in.next();
                    System.out.println("Lesson's name: ");
                    String newLesson = in.next();
                    System.out.println("Student's grade: ");
                    int newGrade = in.nextInt();
                    sql = "INSERT INTO class(name, lesson, grade) VALUES('" + newName + "','" + newLesson + "'," + newGrade + ")";
                    stmt.execute(sql);
                    System.out.println("new information added successfully!");
                    disconncetDb(conn, stmt);
                    break;

                case 3: // Delete info
                    System.out.println("Please enter the Student's ID which you want to DELETE: ");
                    int studentId = in.nextInt();
                    sql = "DELETE FROM class WHERE id=" + studentId;
                    stmt.execute(sql);
                    disconncetDb(conn, stmt);
                    break;

                case 4: // update info
                    System.out.println("What do you want to update? (name, lesson or grade");
                    String answer = in.next();
                    switch (answer) {
                        case "name":
                            System.out.println("Please enter Student's ID which you want to update: ");
                            int updateID = in.nextInt();

                            System.out.println("Enter the name: ");
                            String updateName = in.next();

                            sql = "UPDATE class SET name='" + updateName + "' WHERE id=" + updateID;
                            stmt.execute(sql);
                            System.out.println("Student's name updated by ID of " + updateID);
                            break;
                        case "lesson":
                            System.out.println("Please enter Student's ID which you want to update: ");
                            updateID = in.nextInt();

                            System.out.println("Enter the name: ");
                            String updateLesson = in.next();

                            sql = "UPDATE class SET lesson='" + updateLesson + "' WHERE id=" + updateID;
                            stmt.execute(sql);
                            System.out.println("Student's lesson updated by ID of " + updateID);
                            break;
                        case "grade":
                            System.out.println("Please enter Student's ID which you want to update: ");
                            updateID = in.nextInt();

                            System.out.println("Enter the name: ");
                            int updateGrade = in.nextInt();

                            sql = "UPDATE class SET grade=" + updateGrade + " WHERE id=" + updateID;
                            stmt.execute(sql);
                            System.out.println("Student's grade updated by ID of " + updateID);
                            break;
                        default:
                            System.out.println("Incorrect input, you can choose only between name, lesson or grade.");
                            break;
                    }
                    disconncetDb(conn, stmt);
                    break;
                default: // exit mode
                    System.out.println("OK");
                    break;
            }

        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }

    }

    public static void info() {
        System.out.println(
                "Enter:" +
                        "\n 1: To list all students info" +
                        "\n 2: To add new student info" +
                        "\n 3: To delete student info" +
                        "\n 4: To update student info" +
                        "\n 5: EXIT"
        );
        System.out.println("Your input is: ");
    }

    public static void disconncetDb(Connection conn, Statement stmt) {
        try {
            stmt.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }

        try {
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }

        System.out.println("Disconnected from database.");
    }
}

import java.sql.SQLException;
import java.util.ArrayList;

public interface ThreadCallback {
    void onDataFetched(ArrayList<HomeworkClass> dataSet);

    void onEnd();

    void onError(SQLException ex);
}